JEE Main 13 April 2023 Shift 2 question paper with solutions

JEE Main 13 April 2023 Shift 2: all 90 questions in paper order (Maths, Physics, Chemistry) with the answer key and worked solutions. Free to read; attempt it as a timed 3-hour mock test.

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Maths

Question 1

Maths · Determinants · Single correct

If the system of equations $$2x + y - z = 5$$ $$2x - 5y + \lambda z = \mu$$ $$x + 2y - 5z = 7$$ has infinitely many solutions, then $$(\lambda + \mu)^2 + (\lambda - \mu)^2$$ is equal to

  1. 904
  2. 916
  3. 912
  4. 920

Answer: (b)

Solution

Given system of equations. $$2x + y - z = 5$$ $$2x - 5y + \lambda z = \mu$$ $$x + 2y - 5z = 7$$ For infinite solution $\Delta = 0 = \Delta_1 = \Delta_2 = \Delta_3$ $$\Rightarrow \Delta = \begin{vmatrix} 2 & 1 & -1 \\ 2 & -5 & \lambda \\ 1 & 2 & -5 \end{vmatrix} = 0$$ $$\Rightarrow 51 - 3\lambda = 0$$ $$\Rightarrow \lambda = 17$$ $$\Rightarrow \Delta_3 = \begin{vmatrix} 5 & 2 & 1 \\ \mu & 2 & -5 \\ 7 & 1 & 2 \end{vmatrix} = 0$$ $$\Rightarrow -3(\mu + 13) = 0$$ $$\Rightarrow \mu = -13$$ Now $$(\lambda + \mu)^2 + (\lambda - \mu)^2$$ $$= (17 + 13)^2 + (17 - 13)^2$$ $$= 900 + 16$$ $$= 916$$ Hence this is the correct option.

Question 2

Maths · Binomial Theorem · Single correct

The coefficient of $x^5$ in the expansion of $\left(2x^3 - \frac{1}{3x^2}\right)^5$ is

  1. $\frac{80}{9}$
  2. 9
  3. 8
  4. $\frac{26}{3}$

Answer: (a)

Solution

General term of the binomial expansion of $\left(2x^3 - \frac{1}{3x^2}\right)^5$ is $$T_{r+1} = \binom{5}{r} \left(2x^3\right)^{5-r} \left(-\frac{1}{3x^2}\right)^r$$ $$\Rightarrow T_{r+1} = \binom{5}{r} (2)^{5-r} \left(-\frac{1}{3}\right)^r x^{15-5r}$$ For coefficient of $x^5$, we must have $$15 - 5r = 5 \Rightarrow r = 2$$ So, required coefficient is $$= \binom{5}{2} (2)^3 \left(\frac{1}{9}\right)$$ $$= 10 \times 8 \times \frac{1}{9}$$ $$= \frac{80}{9}$$

Question 3

Maths · Three Dimensional Geometry · Single correct

The plane, passing through the points $(0, -1, 2)$ and $(-1, 2, 1)$ and parallel to the line passing through $(5, 1, -7)$ and $(1, -1, -1)$, also passes through the point

  1. $(-2, 5, 0)$
  2. $(1, -2, 1)$
  3. $(2, 0, 1)$
  4. $(0, 5, -2)$

Answer: (a)

Solution

Let $A(0, -1, 2)$ and $B(-1, 2, 1)$ and given plane is parallel to line passing through $(5, 1, -7)$ and $(1, -1, -1)$. So, normal vector to the plane is given by, $$ \vec{n} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ -1 - 0 & 2 + 1 & 1 - 2 \\ 1 - 5 & -1 - 1 & -1 + 7 \end{vmatrix} $$ $$ \Rightarrow \vec{n} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ -1 & 3 & -1 \\ -4 & -2 & 6 \end{vmatrix} = \hat{i}(16) - \hat{j}(-10) + \hat{k}(14) $$ $$ \Rightarrow \vec{n} = 16\hat{i} + 10\hat{j} + 14\hat{k} $$ Therefore, the equation of the plane is $$ 16(x - 0) + 10(y + 1) + 14(z - 2) = 0 $$ $$ \Rightarrow 8x + 5y + 7z = 9 $$ Now satisfying the points from option in the plane we get, $(-2, 5, 0)$ only point which satisfy the plane.

Question 4

Maths · Complex Numbers and Quadratic Equations · Single correct

Let $\alpha$, $\beta$ be the roots of the equation $x^2 - \sqrt{2}x + 2 = 0$ Then $\alpha^{14} + \beta^{14}$ is equal to

  1. -64
  2. -64$\sqrt{2}$
  3. -128
  4. -128$\sqrt{2}$

Answer: (c)

Solution

Given, $$x^2 - \sqrt{2}x + 2 = 0$$ $$\Rightarrow x = \frac{\sqrt{2} \pm \sqrt{6}i}{2}$$ $$\Rightarrow x = \sqrt{2} \left( \frac{1 \pm \sqrt{3}i}{2} \right)$$ $$\Rightarrow x = \sqrt{2} \left( \frac{1}{2} \pm \frac{\sqrt{3}i}{2} \right)$$ $$\Rightarrow x = \sqrt{2} \left( \cos \frac{\pi}{3} \pm i \sin \frac{\pi}{3} \right)$$ So, $$\alpha = \sqrt{2} \left( \cos \frac{\pi}{3} + i \sin \frac{\pi}{3} \right) = \sqrt{2} e^{i \frac{\pi}{3}}$$ And $$\beta = \sqrt{2} \left( \cos \frac{\pi}{3} - i \sin \frac{\pi}{3} \right) = \sqrt{2} e^{-i \frac{\pi}{3}}$$ Now $$\alpha^{14} + \beta^{14} = \left( \sqrt{2} e^{i \frac{\pi}{3}} \right)^{14} + \left( \sqrt{2} e^{-i \frac{\pi}{3}} \right)^{14}$$ $$\Rightarrow \alpha^{14} + \beta^{14} = \left( \sqrt{2} \right)^{14} \left( e^{i 14 \frac{\pi}{3}} + e^{-i 14 \frac{\pi}{3}} \right)$$ $$\Rightarrow \alpha^{14} + \beta^{14} = \left( \sqrt{2} \right)^{14} \left( \cos \frac{14\pi}{3} + i \sin \frac{14\pi}{3} + \cos \frac{14\pi}{3} - i \sin \frac{14\pi}{3} \right)$$ $$\Rightarrow \alpha^{14} + \beta^{14} = 2^7 \left( 2 \cos \frac{14\pi}{3} \right)$$ $$\Rightarrow \alpha^{14} + \beta^{14} = 2^8 \left( \cos \left( 4\pi + \frac{2\pi}{3} \right) \right)$$ $$\Rightarrow \alpha^{14} + \beta^{14} = 2^8 \left( \cos \frac{2\pi}{3} \right)$$ $$\Rightarrow \alpha^{14} + \beta^{14} = -2^8 \times \frac{1}{2} = -128$$

Question 5

Maths · Sequences and Series · Single correct

Let $a_1, a_2, a_3, \ldots$ be a G.P. of increasing positive numbers. Let the sum of its $6^{th}$ and $8^{th}$ terms be $2$ and the product of its $3^{rd}$ and $5^{th}$ terms be $\frac{1}{9}$. Then $6(a_2 + a_4)(a_4 + a_6)$ is equal to

  1. 3
  2. 3$\sqrt{3}$
  3. 2
  4. 2$\sqrt{2}$

Answer: (a)

Solution

Given, $a_1,a_2,a_3,\ldots$ be a G.P. of increasing positive numbers, and the sum of its $6$th and $8$th terms be $2$. So, $a_6+a_8=2$ $\Rightarrow ar^5+ar^7=2 \qquad \ldots\ (1)$ And the product of its $3$rd and $5$th terms be $\frac{1}{9}$. So, $a_3\cdot a_5=\frac{1}{9}$ $\Rightarrow (ar^2)(ar^4)=\frac{1}{9}$ $\Rightarrow a^2r^6=\frac{1}{9}$ $\Rightarrow (ar^3)^2=\frac{1}{9}$ Since the terms are positive, $\Rightarrow ar^3=\frac{1}{3}$ Now putting the value of $ar^3=\frac{1}{3}$ in equation $(1)$, we get $\frac{r^2}{3}+\frac{r^4}{3}=2$ $\Rightarrow r^4+r^2=6$ $\Rightarrow (r^2+3)(r^2-2)=0$ $\Rightarrow r^2=2$ Also, $ar^3=\frac{1}{3}$ $\Rightarrow ar\cdot r^2=\frac{1}{3}$ $\Rightarrow ar\cdot 2=\frac{1}{3}$ $\Rightarrow ar=\frac{1}{6}$ Now finding the value of $6(a_2+a_4)(a_4+a_6)$, we get $=6(ar+ar^3)(ar^3+ar^5)$ $=6\left(\frac{1}{6}+\frac{1}{3}\right)\left(\frac{1}{3}+\frac{2}{3}\right)$ $=6\cdot\frac{1}{2}\cdot 1$ $=3$.

Question 6

Maths · Straight Lines and Pair of Straight Lines · Single correct

Let $(\alpha, \beta)$ be the centroid of the triangle formed by the lines $15x - y = 82$, $6x - 5y = -4$ and $9x + 4y = 17$. Then $\alpha + 2\beta$ and $2\alpha - \beta$ are the roots of the equation

  1. $x^2 - 7x + 12 = 0$
  2. $x^2 - 14x + 48 = 0$
  3. $x^2 - 13x + 42 = 0$
  4. $x^2 - 10x + 25 = 0$

Answer: (c)

Solution

The given set of equations are: $$15x - y = 82$$ $$6x - 5y = -4$$ $$9x + 4y = 17$$ Now on solving the above equation by taking two at a time and plotting the diagram we get, $$A(1, 2)$$ $$B(5, -7)$$ $$C(6, 8)$$ $$(\alpha, \beta) \equiv \left( \frac{1+5+6}{3}, \frac{2-7+8}{3} \right) \equiv (4, 1)$$ Hence, $\alpha + 2\beta = 6$ and $2\alpha - \beta = 7$ The required equation is $(x - 6)(x - 7) = 0$ Equation $x^2 - 13x + 42 = 0$ Hence this is the required option.

Question 7

Maths · Vector Algebra · Single correct

Let $|\vec{a}|=2$ and $|\vec{b}|=3$, and the angle between the vectors $\vec{a}$ and $\vec{b}$ be $\frac{\pi}{4}$. Then $\left|(\vec{a}+2\vec{b})\times(2\vec{a}-3\vec{b})\right|^2$ is equal to $\underline{\hspace{2cm}}$.

  1. 441
  2. 482
  3. 841
  4. 882

Answer: (d)

Solution

Given, $|\vec{a}| = 2$, $|\vec{b}| = 3$ and the angle between the vectors $\vec{a}$ and $\vec{b}$ be $\frac{\pi}{4}$. Now solving, $$\left| (\vec{a} + 2\, \vec{b}) \times (2\, \vec{a} - 3\, \vec{b}) \right|^2$$ $$= \left| -3 \left( \vec{a} \times \vec{b} \right) + 4 \left( \vec{b} \times \vec{a} \right) \right|^2 \left\{ as \vec{a} \times \vec{a} = 0 and \vec{b} \times \vec{b} = 0 \right\}$$ $$= \left| 7 \left( \vec{b} \times \vec{a} \right) \right|^2 \left\{ as \vec{b} \times \vec{a} = -\vec{a} \times \vec{b} \right\}$$ $$= 49 |a|^2 |b|^2 \sin^2 \frac{\pi}{4}$$ $$= 49 \times 4 \times 9 \times \frac{1}{2}$$ $$= 882$$

Question 8

Maths · Three Dimensional Geometry · Single correct

Let $N$ be the foot of perpendicular from the point $P(1, -2, 3)$ on the line passing through the points $(4, 5, 8)$ and $(1, -7, 5)$. Then the distance of $N$ from the plane $2x - 2y + z + 5 = 0$ is

  1. 8
  2. 6
  3. 9
  4. 7

Answer: (d)

Solution

Given, $N$ be the foot of perpendicular from the point $P(1, -2, 3)$ on the line passing through the points $(4, 5, 8)$ and $(1, -7, 5)$, Now finding direction ratio of line $L$ we get, $$(4 - 1, 5 + 7, 8 - 5) \equiv (3, 12, 3) \equiv (1, 4, 1)$$ Hence, the equation of Line will be, $$L : \frac{x-1}{1} = \frac{y+7}{4} = \frac{z-5}{1} = r$$ Now let point $N \equiv (r + 1, 4r - 7, r + 5)$ And given $P \equiv (1, -2, 3)$ So, direction ratio of $PN(r, 4r - 5, r + 2)$ Since, $PN \perp L$ so by perpendicular condition we get, $$r + 4(4r - 5) + (r + 2) = 0$$ $$\Rightarrow r = 1$$ Hence, $N \equiv (2, -3, 6)$ Now finding, distance of $N(2, -3, 6)$ from plane $2x - 2y + z + 5 = 0$ we get, $$Distance = \frac{|4 + 6 + 6 + 5|}{\sqrt{4 + 4 + 1}} = 7$$

Question 9

Maths · Limits and Derivatives · Single correct

If $\lim_{x \to 0} \frac{e^{ax} - \cos(bx) - \frac{ax - cx}{2}}{1 - \cos(2x)} = 17$, then $5a^2 + b^2$ is equal to

  1. 64
  2. 72
  3. 68
  4. 76

Answer: (c)

Solution

Given that $$ \lim_{x \to 0} \frac{e^{ax} - \cos(bx) - \frac{cx}{2} e^{-cx}}{1 - \cos 2x} = 17 $$ We know that $e^{ax} = 1 + ax + \frac{(ax)^2}{2!} + \ldots$ and $\cos(bx) = 1 - \frac{(bx)^2}{2!} + \ldots$ $$ \Rightarrow \lim_{x \to 0} \frac{\left(1 + ax + \frac{(ax)^2}{2!} + \ldots \right) - \left(1 - \frac{(bx)^2}{2!} + \ldots \right) - \frac{cx}{2} \left(1 - (cx) + \frac{(cx)^2}{2!} - \ldots \right)}{\frac{1 - \cos 2x}{(2x)^2} \times 4x^2} = 17 $$ $$ \Rightarrow \lim_{x \to 0} \frac{\left(a - \frac{c}{2} \right)x + \left(\frac{a^2 + b^2 + c^2}{2} \right)x^2 + \ldots}{\frac{1}{2} \times 4x^2} = 17 $$ Now for limit to exist, $a - \frac{c}{2} = 0 \Rightarrow c = 2a$ $$ \Rightarrow \lim_{x \to 0} \frac{\left(\frac{a^2 + b^2 + c^2}{2} \right)x^2 + \ldots}{\frac{1}{2} \times 4x^2} = 17 $$ $$ \Rightarrow \frac{a^2 + b^2 + c^2}{4} = 17 $$ $$ \Rightarrow a^2 + b^2 + 4a^2 = 68 $$ $$ \Rightarrow 5a^2 + b^2 = 68 $$ Hence this is the correct option.

Question 10

Maths · Conic Sections · Single correct

Let the centre of a circle $C$ be $\alpha$, $\beta$ and its radius $r < 8$. Let $3x + 4y = 24$ and $3x - 4y = 32$ be two tangents and $4x + 3y = 1$ be a normal to $C$. Then $\left(\alpha - \beta + r\right)$ is equal to

  1. 7
  2. 5
  3. 6
  4. 9

Answer: (a)

Solution

Given, the centre of a circle $C$ be $\alpha$, $\beta$ and its radius $r 8$, so neglected. $$\therefore r = 5, \alpha = 1, \beta = -1$$ $$\therefore \alpha - \beta = 7$$

Question 11

Maths · Permutations and Combinations · Single correct

All words, with or without meaning, are made using all the letters of the word MONDAY. These words are written as in a dictionary with serial numbers. The serial number of the word MONDAY is

  1. 327
  2. 328
  3. 324
  4. 326

Answer: (a)

Solution

The given word is MONDAY. Arranging the letters alphabetically, we get ADMNOY. When the word starts with any of the letters A/D, the number of possibilities is $5! \times 2 = 240$. Now when the word starts with MA, the number of possibilities is $4! = 24$. Now when the word starts with MD, the number of possibilities is $4! = 24$. Now when the word starts with MN, the number of possibilities is $4! = 24$. Now when the word starts with MOA, the number of possibilities is $3! = 6$. Now when the word starts with MOD, the number of possibilities is $3! = 6$. Now when the word starts with MONA, the number of possibilities is $2! = 2$. Now when the word starts with MONDAY, the number of possibilities is $1$. Rank $= 240 + 24 \times 3 + 6 \times 2 + 2 + 1 = 327$. Hence, rank of the word MONDAY is 327. SHORTCUT METHOD Another method is a shortcut, first number the alphabet and then check how many numbers are there on the right-hand side less than that number and then start number in factorial in decreasing order and then multiply and add them and in last add one to find rank, $$\begin{array}{cccccc} 3 & 5 & 4 & 2 & 1 & 6 \\ M & O & N & D & A & Y \\ 2 & 3 & 2 & 1 & 0 & 0 \\ 5! & 4! & 3! & 2! & 1! & 0! \end{array}$$ $$\therefore Rank = (2 \times 5! + 3 \times 4! + 2 \times 3! + 1 \times 2!)$$ $$= 240 + 72 + 12 + 2 + 1 = 327$$

Question 12

Maths · Relations and Functions · Single correct

The range of $f(x) = 4 \sin^{-1} \left( \frac{x^2}{x^2+1} \right)$ is

  1. $[0, 2\pi]$
  2. $[0, \pi]$
  3. $[0, 2\pi]$
  4. $[0, \pi]$

Answer: (c)

Solution

Given, $$f(x) = 4 \sin^{-1} \left( \frac{x^2}{x^2+1} \right)$$ Now taking, $$\frac{x^2}{1+x^2} = 1 - \frac{1}{1+x^2} < 1$$ $$\Rightarrow 0 \leq \frac{x^2}{1+x^2} < 1$$ Now taking $\sin^{-1}$ we get, $$\Rightarrow 0 \leq \sin^{-1} \left( \frac{x^2}{1+x^2} \right) < \frac{\pi}{2}$$ $$\Rightarrow 0 \leq 4 \sin^{-1} \left( \frac{x^2}{1+x^2} \right) < 2\pi$$ Hence, the range of $4 \sin^{-1} \left( \frac{x^2}{x^2+1} \right)$ is $[0, 2\pi)$.

Question 13

Maths · Mathematical Reasoning · Single correct

The statement $(p \land (\sim q)) \lor ((\sim p) \land q) \lor ((\sim p) \land (\sim q))$ is equivalent to

  1. $(\sim p) \lor q$
  2. $(\sim p) \lor (\sim q)$
  3. $p \lor (\sim q)$
  4. $p \lor q$

Answer: (b)

Solution

Given, $$(p \land (\sim q)) \lor ((\sim p) \land q) \lor ((\sim p) \land (\sim q))$$ $$= ((\sim p) \land q) \lor ((\sim p) \land (\sim q)) \lor (p \land (\sim q))$$ $$=(\sim p \land (q \lor \sim q)) \lor (p \land \sim q)$$ We know that $\sim A \lor A = T$, where $T$ is tautology, $$=(\sim p \lor T) \lor (p \land \sim q)$$ $$= \sim p \lor (p \land \sim q)$$ $$=(\sim p \lor p) \land (\sim p \lor \sim q)$$ $$= T \land (\sim p \lor \sim q)$$ $$= \sim p \lor \sim q$$

Question 14

Maths · Probability · Single correct

The random variable $X$ follows binomial distribution $B(n, p)$, for which the difference of the mean and the variance is 1. If $2 \cdot P(X = 2) = 3 \cdot P(X = 1)$, then $n^2 P(X > 1)$ is equal to

  1. 15
  2. 11
  3. 12
  4. 16

Answer: (b)

Solution

Given that the difference between the mean and variance is 1. $$np - npq = 1$$ $$np(1 - q) = 1$$ $$np^2 = 1$$ Also given that, $$2P(X = 2) = 3P(X = 1)$$ $$2 \cdot nC_2 p^2 q^{n-2} = 3 \cdot nC_1 p \cdot q^{n-1}$$ $$2 \cdot \frac{n \cdot (n-1)}{2} \cdot p = 3 \cdot n \cdot q$$ $$\Rightarrow (n - 1)p = 3(1 - p)$$ $$\Rightarrow \left(\frac{1}{p^2} - 1\right)p = 3(1 - p)$$ $$\Rightarrow \frac{(1-p)(1+p)}{p} = 3\left(1 - p\right)$$ $$\Rightarrow 1 + p = 3p$$ $$\Rightarrow p = \frac{1}{2}$$ $$\therefore n = 4.$$ Now, $$n^2 P(x > 1) = n^2 (1 - P(x = 1) - P(x = 0)) = 16 \left(1 - 4C_1 \cdot \left(\frac{1}{2}\right)^4 - \left(\frac{1}{2}\right)^4\right) = 11$$ Hence this is the correct option.

Question 15

Maths · Matrices · Single correct

Let for $A = \begin{bmatrix} 1 & 2 & 3 \\ \alpha & 3 & 1 \\ 1 & 1 & 2 \end{bmatrix}$, $|A| = 2$. If $|2 adj(2 adj(2A))| = 32^n$, then $3n + \alpha$ is equal to

  1. 9
  2. 11
  3. 12
  4. 10

Answer: (b)

Solution

Given that $A = \begin{bmatrix} 1 & 2 & 3 \\ \alpha & 3 & 1 \\ 1 & 1 & 2 \end{bmatrix}$. Therefore, $|A| = 2$. This implies $1(6 - 1) - \alpha - 7 = 2$. Thus, $-\alpha - 2 = 2$. So, $\alpha = -4$. Therefore, $|2 \operatorname{adj}(2 \operatorname{adj}(2A))| = 32^n$. We know that $|kA| = k^n |A|$, $\operatorname{adj}(\operatorname{adj}(A)) = |A|^{(n-1)^2}$ and $\operatorname{adj}(kA) = k^{n-1} \operatorname{adj}(A)$. $$= 2^3 |\operatorname{adj}(2 \operatorname{adj}(2A))|$$ $$= 2^3 |2^{3-1} \operatorname{adj}(\operatorname{adj}(2A))|$$ $$= 2^3 \cdot (4)^3 |\operatorname{adj}(\operatorname{adj}(2A))|$$ $$= 2^9 |2A|^{(2)^2}$$ $$= 2^9 \cdot |2A|^4$$ $$= 2^9 \cdot 2^{12} |A|^4$$ $$= 2^{21} \cdot 2^4 = 2^{25} = (32)^n = (2)^5n$$ Therefore, $n = 5$. Thus, $3n + \alpha = 15 - 4 = 11$. Hence this is the correct option.

Question 16

Maths · Complex Numbers and Quadratic Equations · Single correct

Let $S = \{ z \in \mathbb{C} : \bar{z} = i(z^2 + \mathrm{Re}(\bar{z})) \}$. Then $\sum_{z \in S} |z|^2$ is equal to

  1. $\frac{5}{2}$
  2. 4
  3. $\frac{7}{2}$
  4. 3

Answer: (b)

Solution

Given, $$\bar{z} = i \left( z^2 + \mathrm{Re}(z) \right)$$ Now, let $( z = x + iy )$, so $( \bar{z} = x - iy )$. Now putting the value in, $$( \bar{z} = i \left( z^2 + \mathrm{Re}(\bar{z}) \right) )$$ we get, $$\bar{z} = i \left( z^2 + \mathrm{Re}(z) \right)$$ $$\Rightarrow x - iy = i \left( x^2 - y^2 + 2ixy + x \right)$$ $$\Rightarrow x - iy = i \left( x^2 - y^2 + x \right) - 2xy$$ Now comparing real part we get, $$x = -2xy \Rightarrow x(2y + 1) = 0$$ $$\Rightarrow x = 0,\; y = -\frac{1}{2} \ldots (1)$$ And imaginary part we get, $$-y = x^2 - y^2 + x \ldots (2)$$ Now taking Case (I) when $( x = 0 )$ in equation (2) we get, $$\Rightarrow -y = -y^2$$ $$\Rightarrow y^2 - y = 0 \Rightarrow y = 0,\; 1$$ So, $( z = 0,\; i )$ Now taking Case (II) when $( y = -\frac{1}{2} )$ in equation (2) we get, $$\Rightarrow \frac{1}{2} = x^2 - \frac{1}{4} + x$$ $$\Rightarrow x^2 + x - \frac{3}{4} = 0$$ $$\Rightarrow 4x^2 + 4x - 3 = 0$$ $$\Rightarrow (2x - 1)(2x + 3) = 0$$ $$\Rightarrow x = \frac{1}{2},\; -\frac{3}{2}$$ So, $( z = \frac{1}{2} - \frac{1}{2} i,\; \frac{-3}{2} - \frac{1}{2} i )$ Now finding, $$\sum | z^2 | = 0 + 1 + \frac{1}{2} + \frac{5}{2} = 4$$

Question 17

Maths · Applications of Integrals · Single correct

The area of the region $x, y : x^2 \leq y \leq |x^2 - 4|, y \geq 1$ is

  1. $\frac{4}{3} (4\sqrt{2} - 1)$
  2. $\frac{4}{3} (4\sqrt{2} + 1)$
  3. $\frac{3}{4} (4\sqrt{2} + 1)$
  4. $\frac{3}{4} (4\sqrt{2} - 1)$

Answer: (a)

Solution

The required diagram is: The shaded region is symmetric about the $y$-axis. Required area $= 2 \left[ \int_1^2 \sqrt{y} \, dy + \int_2^4 \sqrt{4-y} \, dy \right]$ $$= 2 \left[ \left. \frac{y^{3/2}}{\frac{3}{2}} \right|_1^2 - \left. \frac{2(4-y)^{3/2}}{3} \right|_2^4 \right]$$ $$= \frac{4}{3} \left( 4\sqrt{2} - 1 \right)$$ Hence this is the correct option.

Question 18

Maths · Properties of Triangles · Single correct

Let for a triangle $ABC$ $\overrightarrow{AB} = -2\hat{i} + \hat{j} + 3\hat{k}$ $\overrightarrow{CB} = \alpha \hat{i} + \beta \hat{j} + \gamma \hat{k}$ $\overrightarrow{CA} = 4\hat{i} + 3\hat{j} + \delta \hat{k}$ If $\delta > 0$ and the area of the triangle $ABC$ is $5\sqrt{6}$ then $\overrightarrow{CB} \cdot \overrightarrow{CA}$ is equal to

  1. 60
  2. 54
  3. 108
  4. 120

Answer: (a)

Solution

Given, $\overrightarrow{AB}=-2\hat{i}+\hat{j}+3\hat{k}$ $\overrightarrow{CB}=\alpha\hat{i}+\beta\hat{j}+\gamma\hat{k}$ $\overrightarrow{CA}=4\hat{i}+3\hat{j}+\delta\hat{k}$ Now plotting the diagram we get, Now from triangle law of addition we get, $\overrightarrow{CA}+\overrightarrow{AB}=\overrightarrow{CB}$ $4\hat{i}+3\hat{j}+\delta\hat{k}+(-2\hat{i}+\hat{j}+3\hat{k})=\alpha\hat{i}+\beta\hat{j}+\gamma\hat{k}$ $2\hat{i}+4\hat{j}+(\delta+3)\hat{k}=\alpha\hat{i}+\beta\hat{j}+\gamma\hat{k}$ Now on comparing both sides we get, $\alpha=2,\ \beta=4$ and $\gamma=\delta+3$ Now the area of triangle is given by, $A=\frac{1}{2}\left|\overrightarrow{AB}\times\overrightarrow{CB}\right|$ $\Rightarrow 5\sqrt{6}=\sqrt{(\gamma-12)^2+(6+2\gamma)^2+100}$ Squaring both sides, $150=(\gamma-12)^2+(6+2\gamma)^2+100$ $\Rightarrow 150=\gamma^2-24\gamma+144+4\gamma^2+24\gamma+36+100$ $\Rightarrow 5\gamma^2=320$ $\Rightarrow \gamma^2=64\Rightarrow\gamma=8$ So, $\delta=8-3=5$ Also, $\overrightarrow{CB}\cdot\overrightarrow{CA}=(\alpha\hat{i}+\beta\hat{j}+\gamma\hat{k})\cdot(4\hat{i}+3\hat{j}+\delta\hat{k})$ $\Rightarrow \overrightarrow{CB}\cdot\overrightarrow{CA}=(2\hat{i}+4\hat{j}+8\hat{k})\cdot(4\hat{i}+3\hat{j}+5\hat{k})$ $=8+12+40=60$

Question 19

Maths · Three Dimensional Geometry · Single correct

The line, that is coplanar to the line $\frac{x+3}{-3} = \frac{y-1}{1} = \frac{z-5}{5}$, is

  1. $\frac{x+1}{-1} = \frac{y-2}{2} = \frac{z-5}{4}$
  2. $\frac{x+1}{-1} = \frac{y-2}{2} = \frac{z-5}{5}$
  3. $\frac{x-1}{-1} = \frac{y-2}{2} = \frac{z-5}{5}$
  4. $\frac{x+1}{1} = \frac{y-2}{2} = \frac{z-5}{5}$

Answer: (b)

Solution

We know that two lines $\frac{x-x_1}{a_1} = \frac{y-y_1}{b_1} = \frac{z-z_1}{c_1}$ and $\frac{x-x_2}{a_2} = \frac{y-y_2}{b_2} = \frac{z-z_2}{c_2}$ are coplanar if $$\begin{vmatrix} x_2 - x_1 & y_2 - y_1 & z_2 - z_1 \\ a_1 & b_1 & c_1 \\ a_2 & b_2 & c_2 \end{vmatrix} = 0$$ Let us verify this option. The given lines are $\frac{x+3}{-3} = \frac{y-1}{1} = \frac{z-5}{5}$ and $\frac{x+1}{-1} = \frac{y-2}{2} = \frac{z-5}{5}$. $$= \begin{vmatrix} -1 & -(-3) & 2 & -1 & 5 & -5 \\ -3 & 1 & 5 \\ -1 & 2 & 5 \end{vmatrix}$$ $$= \begin{vmatrix} 2 & 1 & 0 \\ -3 & 1 & 5 \\ -1 & 2 & 5 \end{vmatrix}$$ $$= 2(5 - 10) - (1)(-15 - (-5)) + 0$$ $$= 2(-5) + (10) = 0$$ Therefore, this is the correct option.

Question 20

Maths · Integrals · Single correct

The value of \[ \frac{e^{\frac{\pi}{4}} + \int_{0}^{\pi} e^{-x} \tan^{50} x \, dx}{\int_{0}^{\pi} e^{-x} \left( \tan^{49} x + \tan^{51} x \right) \, dx} \]

  1. 51
  2. 50
  3. 25
  4. 49

Answer: (b)

Solution

Let, $$I = \frac{e^{-\frac{\pi}{4}} + \int_{0}^{\frac{\pi}{4}} e^{-x} \tan^{50} x \, dx}{\int_{0}^{\frac{\pi}{4}} e^{-x} (\tan^{49} x + \tan^{51} x) \, dx}$$ Now let $I_1 = \int_{0}^{\frac{\pi}{4}} e^{-x} (\tan^{49} x + \tan^{51} x) \, dx$. Now solving, $I_2 = \int_{0}^{\frac{\pi}{4}} e^{-x} \tan^{50} x \, dx$ using by parts we get, $$I_2 = \int_{0}^{\frac{\pi}{4}} e^{-x} \tan^{50} x \, dx$$ $$\Rightarrow I_2 = \left[ -e^{-x} \tan^{50} x \right]_{0}^{\frac{\pi}{4}} - \int_{0}^{\frac{\pi}{4}} 50 \tan^{49} x \sec^2 x (-e^{-x}) \, dx$$ $$\Rightarrow I_2 = -e^{-\frac{\pi}{4}} + \int_{0}^{\frac{\pi}{4}} 50 \tan^{49} x (1 + \tan^2 x) e^{-x} \, dx$$ $$\Rightarrow I_2 = -e^{-\frac{\pi}{4}} + 50 \int_{0}^{\frac{\pi}{4}} (\tan^{49} x + \tan^{51} x) e^{-x} \, dx$$ $$\Rightarrow I_2 = -e^{-\frac{\pi}{4}} + 50 I_1$$ $$\Rightarrow \int_{0}^{\frac{\pi}{4}} e^{-x} \tan^{50} x \, dx + e^{-\frac{\pi}{4}} = 50 I_1$$ Now putting the given integral $I$ we get, $$I = \frac{e^{-\frac{\pi}{4}} + \int_{0}^{\frac{\pi}{4}} e^{-x} \tan^{50} x \, dx}{\int_{0}^{\frac{\pi}{4}} e^{-x} (\tan^{49} x + \tan^{51} x) \, dx}$$ $$\Rightarrow I = \frac{50 I_1}{I_1} = 50$$

Question 21

Maths · Statistics · Numerical

The mean and standard deviation of the marks of 10 students were found to be 50 and 12 respectively. Later, it was observed that two marks 20 and 25 were wrongly read as 45 and 50 respectively. Then the correct variance is

Answer: 269

Solution

Let the observations be $x_1, x_2, x_3, \ldots, x_8, 45, 50$. Mean $= 50$ implies $$\frac{x_1 + x_2 + x_3 + \ldots + x_8 + 45 + 50}{10} = 50$$ which implies $$x_1 + x_2 + x_3 + \ldots + x_8 = 405 \ldots (i)$$ Hence, new mean $$\left(\overline{X}\right)_{new} = \frac{405 + 20 + 25}{10} = 45$$ Now, $$S. D = \sqrt{\frac{\sum_{i=1}^{8} x_i^2 + 45^2 + 50^2}{10} - (50)^2}$$ implies $$12 = \sqrt{\frac{\sum_{i=1}^{8} x_i^2 + 4525}{10} - 2500}$$ which implies $$\sum_{i=1}^{8} x_i^2 = 21915$$ Now, $$(Variance)_{new} = \frac{\sum_{i=1}^{8} x_i^2 + 20^2 + 25^2}{10} - (45)^2$$ implies $$(Variance)_{new} = \frac{21915 + 202 + 252}{10} - (45)^2$$ which implies $$(Variance)_{new} = 2294 - 2025$$ which implies $$(Variance)_{new} = 269$$ Hence this is the correct answer.

Question 22

Maths · Relations and Functions · Numerical

Let $A = \{-4, -3, -2, 0, 1, 3, 4\}$ and $R = \{(a, b) \in A \times A : b = |a| or b^2 = a + 1\}$ be a relation on $A$. Then the minimum number of elements, that must be added to the relation $R$ so that it becomes reflexive and symmetric, is

Answer: 7

Solution

Given, $A = \{-4, -3, -2, 0, 1, 3, 4\}$ and $R = \{(a, b) \in A \times A : b = |a| or b^2 = a + 1\}$ be a relation on $A$, So, the relation is given by, $$R = \{(-4, 4), (-3, 3), (0, 0), (1, 1), (3, 3), (4, 4), (0, 1), (3, -2)\}$$ Now, relation to be reflexive $(a, a) \in R \forall a \in A$ $$\Rightarrow (-4, -4), (-3, -3), (-2, -2) also should be added in R.$$ Now relation to be symmetric if $(a, b) \in R$, then $(b, a) \in R \forall a, b \in A$ $$\Rightarrow (4, -4), (3, -3), (1, 0), (-2, 3) also should be added in R$$ Hence, minimum number of elements to be added to $$R = 3 + 4 = 7$$

Question 23

Maths · Sequences and Series · Numerical

Let $f(x) = \sum_{k=1}^{10} k \cdot x^k$, $x \in \mathbb{R}$, if $2f(2) + f'(2) = 119(2)^n + 1$ then $n$ is equal to ______.

Answer: 10

Solution

Given, $$f(x) = \sum_{k=1}^{10} k \cdot x^k, \; x \in \mathbb{R}$$ Thus, $$f(x) = x + 2x^2 + 3x^3 + \ldots + 10x^{10}$$ Now let $$S = x + 2x^2 + 3x^3 + \ldots + 10x^{10}$$ So, $$S \cdot x = x^2 + 2x^3 + \ldots + 9x^{10} + 10x^{11}$$ Now subtracting above equations we get, $$S(1-x) = x + x^2 + x^3 + \ldots + x^{10} - 10x^{11}$$ Thus, $$S(1-x) = \frac{x(1-x^{10})}{1-x} - 10x^{11}$$ Thus, $$S = \frac{x(1-x^{10})}{(1-x)^2} - \frac{10x^{11}}{1-x} = f(x)$$ Now finding, $$f(2) = 2(1-2^{10}) + 10 \cdot 2^{11}$$ Thus, $$f(2) = 2 + 18 \cdot 2^{10}$$ Now finding $f'(x)$ we get, $$f'(x) = \frac{-10x^{11}}{(1-x)^2} - \frac{110x^{10}}{1-x} + \frac{10x^{10}}{(1-x)^2} + \frac{2x(1-x^{10})}{(1-x)^3} + \frac{1-x^{10}}{(1-x)^2}$$ Thus, $$f'(2) = \frac{-10 \cdot 2^{11}}{(1-2)^2} - \frac{110 \cdot 2^{10}}{1-2} - \frac{10 \cdot 2^{10}}{(1-2)^2}$$ Thus, $$f'(2) = -10 \cdot 2^{11} + 110 \cdot 2^{10} - 10 \cdot 2^{10}$$ Thus, $$f'(2) = 83 \cdot 2^{10} - 3$$ Thus, $$2f(2) + f'(2) = 2(2 + 18 \cdot 2^{10}) + 83 \cdot 2^{10} - 3 = 119(2)^{10} + 1$$ Therefore, $$n = 10$$

Question 24

Maths · Permutations and Combinations · Numerical

Total numbers of 3-digit numbers that are divisible by 6 and can be formed by using the digits 1, 2, 3, 4, 5 with repetition, is

Answer: 16

Solution

A number is divisible by 6 when it is divisible by 2 and 3 both. The three digit number can be $ab2$. $a + b$ can be 4, 7, 10. If $a + b = 4$ then $(a, b)$ can be $(1, 3)$, $(3, 1)$, $(2, 2)$. If $a + b = 7$ then $(a, b)$ can be $(2, 5)$, $(5, 2)$, $(3, 4)$, $(4, 3)$. If $a + b = 10$ then $(a, b)$ can be $(5, 5)$. So, 8 such cases when 2 is at unit's place. Similarly, there exist 8 such cases when 4 is at unit's place. Total $= 16$ cases. Hence this is the required answer.

Question 25

Maths · Sequences and Series · Numerical

Let $[\alpha]$ denote the greatest integer $\leq \alpha$. Then $[\sqrt{1}] + [\sqrt{2}] + [\sqrt{3}] + \cdots + [\sqrt{120}]$ is equal to

Answer: 825

Solution

Given, $\($ $\left$$\lfloor$ $\sqrt{1}$ $\right$$\rfloor$ + $\left$$\lfloor$ $\sqrt{2}$ $\right$$\rfloor$ + $\left$$\lfloor$ $\sqrt{3}$ $\right$$\rfloor$ + $\ldots$ + $\left$$\lfloor$ $\sqrt{120}$ $\right$$\rfloor$ $\)$ Now we know that, $\($ $\left$$\lfloor$ $\sqrt{x}$ $\right$$\rfloor$ = 1 $\)$, when $\($ x $\in$ [1, 4) $\)$, $\($ $\left$$\lfloor$ $\sqrt{x}$ $\right$$\rfloor$ = 2 $\)$, when $\($ x $\in$ [4, 9) $\)$ and similarly $\($ $\left$$\lfloor$ $\sqrt{x}$ $\right$$\rfloor$ = 10 $\)$, when $\($ x $\in$ [100, 120) $\)$ Now using the above formula we get, $\($ E = 1 + 1 + 1 + 2 + 2 + 2 + 2 + 2 + 3 + 3 + 3 + 3 + 3 + 3 + 4 + 4 + $\ldots$ $\)$ $\($ $\Rightarrow$ E = 3 $\times$ 1 + 5 $\times$ 2 + 7 $\times$ 3 + $\ldots$ + 19 $\times$ 9 + 10 $\times$ 21 $\)$ $\($ $\Rightarrow$ E = $\sum$_{r=1}^{10} (2r + 1)r $\)$ $\($ $\Rightarrow$ E = 2 $\sum$_{r=1}^{10} (r^2 + r) $\)$ $\($ $\Rightarrow$ E = 2 $\left$[ $\frac{10 \times 11 \times 21}{6}$ $\right$] + $\frac{10 \times 11}{2}$ $\)$ $\($ $\Rightarrow$ E = 770 + 55 $\)$ $\($ $\Rightarrow$ E = 825 $\)$

Question 26

Maths · Inverse Trigonometric Functions · Numerical

For $x \in (-1, 1]$, the number of solutions of the equation $\sin^{-1} x = 2 \tan^{-1} x$ is equal to

Answer: 2

Solution

Given that $\sin^{-1} x = 2 \tan^{-1} x$ $$\Rightarrow \sin^{-1} x = \sin^{-1} \left( \frac{2x}{1+x^2} \right)$$ $$\Rightarrow x = \left( \frac{2x}{1+x^2} \right)$$ $$\Rightarrow x + x^3 = 2x$$ $$\Rightarrow x^3 - x = 0$$ $$\Rightarrow x (x^2 - 1) = 0$$ $$\Rightarrow x = 0, -1, 1.$$ But $x \in (-1, 1]$, so the number of roots are 2, $x = 0 \& 1$

Question 27

Maths · Differential Equations · Numerical

If $y = y(x)$ is the solution of the differential equation $\frac{dy}{dx} + \frac{4x}{(x^2-1)} y = \frac{x+2}{(x^2-1)^{\frac{5}{2}}}, x > 1$ such that $y(2) = \frac{2}{9} \log_e \left( 2 + \sqrt{3} \right)$ and $$y\left( \sqrt{2} \right) = \alpha \log_e \left( \sqrt{\alpha} + \beta \right) + \beta - \sqrt{\gamma}, \alpha, \beta, \gamma \in \mathbb{N},$$ then $\alpha \beta \gamma$ is equal to

Answer: 6

Solution

Given differential equation is $\frac{dy}{dx} + \frac{4x}{(x^2-1)^{5/2}} y = \frac{x+2}{(x^2-1)^{5/2}}, \; x > 1$. Now IF $e^{\int \frac{4x}{x^2-1} dx} = (x^2-1)^2$. The required equation will be $\Rightarrow y \cdot (x^2-1)^2 = \int \frac{x+2}{(x^2-1)^{1/2}} dx$. $$\Rightarrow y \cdot (x^2-1)^2 = \frac{1}{2} \int \frac{2x}{(x^2-1)^{1/2}} dx + 2 \int \frac{dx}{(x^2-1)^{1/2}}$$ $$\Rightarrow y \cdot (x^2-1)^2 = 2 \ln \left( \sqrt{x^2-1} + x \right) + \sqrt{x^2-1} + C$$ Now using, at $x = 2, \; y\left(2\right) = \frac{2}{9} \log_e \left(2 + \sqrt{3}\right)$ we get, $$\Rightarrow 9 \cdot \frac{2}{9} \ln \left(2 + \sqrt{3}\right) = 2 \ln \left(2 + \sqrt{3}\right) + \sqrt{3} + C$$ $$\Rightarrow C = -\sqrt{3}$$ Now finding the value of function at $x = \sqrt{2}$ we get, $$y \times 1 = 2 \ln \left(1 + \sqrt{2}\right) + 1 - \sqrt{3}$$ Now on comparing we get, $$\Rightarrow \beta = 1, \; \alpha = 2, \; \gamma = 3$$ $$\Rightarrow \alpha \beta \gamma = 1 \times 2 \times 3 = 6$$ Hence, this is the required answer.

Question 28

Maths · Conic Sections · Numerical

The foci of a hyperbola are $(\pm 2, 0)$ and its eccentricity is $\frac{3}{2}$. A tangent, perpendicular to the line $2x + 3y = 6$, is drawn at a point in the first quadrant on the hyperbola. If the intercepts made by the tangent on the $x$- and $y$-axes are $a$ and $b$ respectively, then $|6a| + |5b|$ is equal to

  1. 30
  2. 36
  3. 42
  4. 48

Answer: 12

Solution

The given equation of hyperbola is \[ \frac{x^2}{a^2}-\frac{y^2}{b^2}=1,\qquad ae=2,\qquad e=\frac{3}{2} \] \[ \Rightarrow a=\frac{4}{3} \] \[ \Rightarrow b^2=a^2e^2-a^2 =4-\frac{16}{9} =\frac{20}{9} \] The tangent is perpendicular to \[ 2x+3y=6. \] Slope of tangent is \[ m=-\frac{1}{-\frac{2}{3}}=\frac{3}{2}. \] Equation of tangent for slope \(m=\frac{3}{2}\) is \[ y=mx-\sqrt{a^2m^2-b^2}. \] \[ \Rightarrow y=\frac{3}{2}x-\sqrt{\frac{16}{9}\times\frac{9}{4}-\frac{20}{9}} \] \[ (\because\ \text{Tangent is in the first quadrant} \Rightarrow C<0) \] \[ \Rightarrow y=\frac{3}{2}x-\frac{4}{3} \] Converting the equation into intercept form: \[ \frac{x}{\left(\frac{8}{9}\right)}+\frac{y}{\left(-\frac{4}{3}\right)}=1 \] \[ \Rightarrow |6a|+|5b| =\left|\frac{6\times 8}{9}\right| +\left|\frac{5\times(-4)}{3}\right| =12 \] Hence, this is the required option.

Question 29

Maths · Integrals · Numerical

Let $f_n = \int_0^{\frac{\pi}{2}} \left( \sum_{k=1}^{n} \sin^{k-1} x \right) \left( \sum_{k=1}^{n} (2k-1) \sin^{k-1} x \right) \cos x \, dx, \ n \in \mathbb{N}$. Then $f_{21} - f_{20}$ is equal to

Answer: 41

Solution

Given, $$f_n = \int_0^{\pi/2} \left( \sum_{k=1}^n \sin^{k-1} x \right) \left( \sum_{k=1}^n (2k-1) \sin^{k-1} x \right) \cos x \, dx$$ Now let, $\sin x = t$ $$\Rightarrow \cos x \, dx = dt$$ So, $$f_n = \int_0^1 \left( \sum_{k=1}^n (t)^{k-1} \right) \left( \sum_{k=1}^n (2k-1) \right) dt$$ $$\Rightarrow f_n = \int_0^1 \left( 1 + t + t^2 + \ldots + t^{n-1} \right) \left( 1 + 3 + 5t^2 + \ldots + (2n-1)t^{n-1} \right) dt$$ Now multiply and divide by $\sqrt{t}$ we get, $$\Rightarrow f_n = \int_0^1 \left( \frac{1}{t^{\frac{1}{2}} + t^{\frac{3}{2}} + t^{\frac{5}{2}} + \ldots + t^{\frac{2n-1}{2}}} \right) \left( 1 + 3t + 5t^2 + \ldots + (2n-1)t^{n-1} \right) dt$$ $$\Rightarrow f_n = \int_0^1 \left( t^{\frac{1}{2}} + t^{\frac{3}{2}} + t^{\frac{5}{2}} + \ldots + t^{\frac{2n-1}{2}} \right) \left( t^{\frac{-1}{2}} \right) \left( 1 + 3t^{\frac{1}{2}} + 5t^{\frac{3}{2}} + \ldots + (2n-1)t^{\frac{2n-3}{2}} \right) dt$$ Now let $t^{\frac{1}{2}} + t^{\frac{3}{2}} + t^{\frac{5}{2}} + \ldots + t^{\frac{2n-1}{2}} = z$ $$\Rightarrow \left( t^{\frac{-1}{2}} + 3t^{\frac{1}{2}} + 5t^{\frac{3}{2}} + \ldots + (2n-1)t^{\frac{2n-3}{2}} \right) dt = dz$$ Hence, the integral becomes, $$f_n = 2 \int_0^1 z \, dz$$ $$= \left[ z^2 \right]_0^1 = n^2$$ Hence, $$f_{21} = 21^2 - 20^2 = 41$$

Question 30

Maths · Binomial Theorem · Numerical

The remainder, when $7^{103}$ is divided by 17, is

Answer: 12

Solution

Using the binomial expansion in $7^{103} = (7^2)^{51} \cdot 7 = (51 - 2)^{51} \cdot 7$ we get, $$(51 - 2)^{51} \cdot 7 = 7 \cdot \left( {}^{51}C_{0} 51^{51} \cdot 2^0 - {}^{51}C_{1} 51^{50} \cdot 2^1 + \ldots - {}^{51}C_{51} 2^{51} \right)$$ Now 51 is divisible by 17, so when above equation is divided by 17 we get, $7 \cdot (-2^{51})$ as remainder, $$-56(17 - 1)^{12} = -56(2^{4})^{12} = -56(17 - 1)^{12}$$ we get, $$-56(17 - 1)^{12} = -56 \left( {}^{12}C_{0} 17^{12} \cdot 1^0 - {}^{12}C_{1} 17^{11} \cdot 1^1 + \ldots + {}^{12}C_{12} 1^{12} \right)$$ Now dividing above equation by 17 we get, $$(-56 \times 1) \div 17 = -5,$$ Now changing negative remainder to positive we get, $$-5 + 17 = 12,$$ Hence, when $7^{103}$ divided by 17 gives 12 as remainder.

Physics

Question 31

Physics · Nuclei · Single correct

Given below are two statements: one is labelled as Assertion $\textbf{A}$ and the other is labelled as Reason $\textbf{R}$ Assertion $\textbf{A}$ : The binding energy per nucleon is practically independent of the atomic number for nuclei of mass number in the range 30 to 170. Reason $\textbf{R}$ : Nuclear force is short ranged. In the light of the above statements, choose the correct answer from the options given below

  1. A is false but R is true
  2. Both A and R are true and R is the correct explanation of A
  3. Both A and R are true but R is NOT the correct explanation of A
  4. A is true but R is false

Answer: (b)

Solution

The binding energy for stable nuclei is always a positive number, as the nucleus must gain energy for the nucleons to move apart from each other. Nucleons are attracted to each other by the strong nuclear force. Binding energy per nucleon is almost constant in the range of $30 - 170$. This is because nuclear energy is a short range force. It operates in the femto metre region. Hence, this option is the correct one.

Question 32

Physics · Semiconductor Electronics: Materials, Devices and Simple Circuits · Single correct

The output from a NAND gate having inputs A and B given below will be,

Answer: (b)

Solution

The output of NAND gate is $Y = (AB)'$. The truth table is $$ \begin{array}{ccc} A & B & Y \\ 0 & 0 & 1 \\ 0 & 1 & 1 \\ 1 & 0 & 1 \\ 1 & 1 & 0 \\ \end{array} $$ $Y$ would be zero only when both $A$ and $B$ are 1. Clearly, for all other input conditions the output will be 1. Hence, this is the right option.

Question 33

Physics · Electrostatic Potential and Capacitance · Single correct

In the network shown below, the charge accumulated in the capacitor in steady state will be:

  1. 10.3 $\mu$ $\mathrm{C}$
  2. 4.8 $\mu$ $\mathrm{C}$
  3. 12 $\mu$ $\mathrm{C}$
  4. 7.2 $\mu$ $\mathrm{C}$

Answer: (d)

Solution

In steady state, capacitor behaves as open circuit, so no current will flow. The total resistance of the circuit is, $R = (6 + 4) \, \Omega = 10 \, \Omega$. The current flowing through the circuit is $$I = \frac{3 \, \mathrm{V}}{10 \, \Omega}$$ Potential difference on $6 \, \Omega$ resistor $$V' = \frac{3}{10} \times 6 = 1.8 \, \mathrm{V}$$ The charge on the capacitor is, $$Q = CV' = 4 \, \mu \mathrm{F} \times 1.8 \, \mathrm{V} = 7.2 \, \mu \mathrm{C}$$

Question 34

Physics · Gravitation · Single correct

Given below are two statements: Statement I : For a planet, if the ratio of mass of the planet to its radius increase, the escape velocity from the planet also increase. Statement II : Escape velocity is independent of the radius of the planet. In the light of above statements, choose the most appropriate answer from the options given below

  1. Statement I is incorrect but Statement II is correct
  2. Statement I is correct but statement II is incorrect
  3. Both Statement I and Statement II are incorrect
  4. Both Statement I and Statement II are correct

Answer: (b)

Solution

The escape velocity is given by the formula $$v_{esc} = \sqrt{\frac{2GM}{R}}$$ Clearly, the escape velocity depends on the mass and radius of the planet. Hence, if the ratio increases the escape velocity also increases. So, Statement I is correct while statement II is wrong.

Question 35

Physics · Oscillations · Single correct

A particle executes SHM of amplitude $A$. The distance from the mean position when its kinetic energy becomes equal to its potential energy is:

  1. $\frac{1}{\sqrt{2}} A$
  2. $\frac{2A}{2}$
  3. $\sqrt{2} A$
  4. $\frac{1}{2} A$

Answer: (a)

Solution

The potential energy is given by $$U = \frac{m \omega^2 x^2}{2}$$ The kinetic energy is given by $K = \frac{m \omega^2 (A^2 - x^2)}{2}$. Using the condition that $K = U$, $$\frac{1}{2} m \omega^2 (A^2 - x^2) = \frac{1}{2} m \omega^2 x^2$$ $$\Rightarrow x = \frac{A}{\sqrt{2}}$$

Question 36

Physics · Motion in a Straight Line · Single correct

A passenger sitting in a train A moving at $90 \, \mathrm{km} \, \mathrm{h}^{-1}$ observes another train B moving in the opposite direction for $8 \, \mathrm{s}$. If the velocity of the train B is $54 \, \mathrm{km} \, \mathrm{h}^{-1}$, then length of train B is:

  1. 120 $\mathrm{m}$
  2. 320 $\mathrm{m}$
  3. 80 $\mathrm{m}$
  4. 200 $\mathrm{m}$

Answer: (b)

Solution

Let the velocity of A be $v_A$ and the velocity of B be $v_B$. The relative velocity is $$\vec{v}_{BA} = \vec{v}_B - \vec{v}_A$$ $$\Rightarrow v_{BA} = 54 - (-90) = 144 \, \mathrm{km \, h^{-1}}$$ $$\Rightarrow v_{BA} = 40 \, \mathrm{m \, s^{-1}}$$ Time $= \frac{length}{v_{BA}}$ $$\Rightarrow length = 40 \, \mathrm{m \, s^{-1}} \times 8 \, \mathrm{s} = 320 \, \mathrm{m}$$

Question 37

Physics · Thermodynamics · Single correct

The initial pressure and volume of an ideal gas are $P_0$ and $V_0$. The final pressure of the gas when the gas is suddenly compressed to volume $\frac{V_0}{4}$ will be: (Given $\gamma=$ ratio of specific heats at constant pressure and at constant volume.)

  1. $P_0(4)^\gamma$
  2. $4P_0$
  3. $P_0$
  4. $P_0 \left( 4 \right)^{\frac{1}{\gamma}}$

Answer: (a)

Solution

As the gas is suddenly compressed the process is adiabatic. So, $PV^\gamma = constant$. $$P_0 V_0^\gamma = P \cdot \left( \frac{V_0}{4} \right)^\gamma$$ $$\Rightarrow P = 4^\gamma \cdot P_0$$

Question 38

Physics · Mechanical Properties of Fluids · Single correct

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: A spherical body of radius $(5 \pm 0.1) \, \mathrm{mm}$ having a particular density is falling through a liquid of constant density. The percentage error in the calculation of its terminal velocity is $4\%$. Reason R: The terminal velocity of the spherical body falling through the liquid is inversely proportional to its radius. In the light of the above statements, choose the correct answer from the options given below

  1. Both A and R are true and R is the correct explanation of A
  2. Both A and R are true but R is NOT the correct explanation of A
  3. A is true but R is false
  4. A is false but R is true

Answer: (c)

Solution

The terminal velocity is $$V_T = \frac{2}{9} r^2 g \frac{(\rho - \rho')}{\eta}$$ which implies $$V_T \propto r^2$$ Differentiating and dividing by $V_T$, $$\Rightarrow \frac{dV_T}{V_T} = 2 \frac{dr}{r} = 2 \times \frac{0.1}{5}$$ So, the percentage error is $$\frac{dV_T}{V_T} \times 100 = \frac{0.2}{5} \times 100 = 4\%$$ As can be seen the terminal velocity is directly proportional to the square of the radius. Hence $A$ is true but $R$ is false.

Question 39

Physics · Electromagnetic Waves · Single correct

In an electromagnetic wave, at an instant and at a particular position, the electric field is along the negative z-axis and magnetic field is along the positive x-axis. Then the direction of propagation of electromagnetic wave is:

  1. positive z-axis
  2. positive y-axis
  3. at $45^\circ$ angle from positive $y$-axis
  4. negative y-axis

Answer: (d)

Solution

Direction of propagation of the electromagnetic wave is along $\vec{E} \times \vec{B}$. Thus, $$\vec{n} = E \left( -\hat{k} \right) \times B \left( \hat{i} \right)$$ Therefore, $$\hat{n} = -\hat{k} \times \hat{i} = -\hat{j}$$

Question 40

Physics · Motion in a Straight Line · Single correct

The distance travelled by an object in time $t$ is given by $s = (2.5)t^2$. The instantaneous speed of the object at $t = 5 \, \mathrm{s}$ will be:

  1. $25 \, \mathrm{m \, s^{-1}}$
  2. $5 \, \mathrm{m \, s^{-1}}$
  3. $62.5 \, \mathrm{m \, s^{-1}}$
  4. $12.5 \, \mathrm{m \, s^{-1}}$

Answer: (a)

Solution

It is given that $$s = 2.5t^2$$ Differentiating, $$v = \frac{ds}{dt} = \frac{d\left(2.5t^2\right)}{dt} = 5t$$ At $t = 5 \, \mathrm{s}$, $v = 25 \, \mathrm{m \, s^{-1}}$

Question 41

Physics · Moving Charges and Magnetism · Multiple correct

An electron is moving along the positive x-axis. If uniform magnetic field is applied parallel to the negative z-axis, then

  1. A and E only
  2. C and D only
  3. B and E only
  4. B and D only

Answer: (c)

Solution

The Lorentz force is given by $$\vec{F} = q \vec{v} \times \vec{B}$$ $$= -e \vec{v} \times \vec{B}$$ So, $$\vec{F} = \hat{i} \times \hat{k} = -\hat{j}.$$ $$\vec{F}$$ is along the negative $y$ axis. As the magnetic field is perpendicular to the velocity, motion would be circular.

Question 42

Physics · Gravitation · Single correct

Two planets A and B of radii $R$ and $1.5 \, R$ have densities $\rho$ and $\frac{\rho}{2}$ respectively. The ratio of acceleration due to gravity at the surface of B to A is:

  1. 2 : 3
  2. 2 : 1
  3. 3 : 4
  4. 4 : 3

Answer: (c)

Solution

The acceleration due to gravity is $$g = \frac{GM}{R^2} = \frac{4 \pi G R \rho}{3}$$ which implies $$g \propto \rho \cdot R$$ Thus, the ratio is $$\Rightarrow \frac{g_B}{g_A} = \frac{1.5 R \rho}{2 \rho R} = \frac{1}{2} \times 1.5 = 0.75$$ $$\Rightarrow \frac{g_B}{g_A} = \frac{3}{4}$$

Question 43

Physics · Alternating Current · Single correct

Given below are two statements: Statement I : An AC circuit undergoes electrical resonance if it contains either a capacitor or an inductor. Statement II: An AC circuit containing a pure capacitor or a pure inductor consumes high power due to its non-zero power factor. In the light of above statements, choose the correct answer from the options given below:

  1. Statement I is false but statement II is true
  2. Statement I is true but statement II is false
  3. Both Statement I and Statement II are false
  4. Both Statement I and Statement II are true

Answer: (c)

Solution

For resonance to occur the condition is $X_L = X_C$. So, both inductor and capacitor is required. The power factor is given by $\cos \phi$. For an inductor the power factor is zero-lagging, $\cos 90^\circ = 0$. The angle between the voltage and current is $90^\circ$. For a capacitor the power factor is zero-leading. Hence, both statements are false.

Question 44

Physics · Motion in a Plane · Single correct

A vehicle of mass 200 kg is moving along a levelled curved road of radius 70 m with angular velocity of 0.2 rad s^{-1}. The centripetal force acting on the vehicle is:

  1. 560 N
  2. 2800 N
  3. 2240 N
  4. 14 N

Answer: (a)

Solution

The centripetal force is given by $$F = \frac{Mv^2}{R} = MR\omega^2$$ The given data is $$M = 200 \, \mathrm{kg}$$ $$R = 70 \, \mathrm{m}$$ $$\omega = 0.2 \, \mathrm{rad} \, \mathrm{s}^{-1}$$ The magnitude of the force is $$F = 200 \times 70 \times 0.2^2 \, \mathrm{N}$$ $$\Rightarrow F = 560 \, \mathrm{N}$$

Question 45

Physics · Communication Systems · Single correct

To radiate EM signal of wavelength $\lambda$ with high efficiency, the antennas should have a minimum size equal to:

  1. $2\lambda$
  2. $\frac{\lambda}{2}$
  3. $\frac{\lambda}{4}$
  4. $\lambda$

Answer: (c)

Solution

For efficient radiation and reception, the height of transmitting and receiving antennas should be comparable to a quarter of wavelength of the frequency used. So for efficient transmission of signals of wavelengths $\lambda$ the minimum length of antenna should be $\frac{\lambda}{4}$.

Question 46

Physics · Electromagnetic Waves · Single correct

Given below are two statements: Statement I : Out of microwaves, infrared rays and ultraviolet rays, ultraviolet rays are the most effective for the emission of electrons from a metallic surface Statement II : Above the threshold frequency, the maximum kinetic energy of photoelectrons is inversely proportional to the frequency of the incident light In the light of above statements, choose the correct answer from the options given below

  1. Statement I is false but Statement II is true
  2. Statement I is true but Statement II is false
  3. Both Statement I and Statement II are true
  4. Both Statement I and Statement II are false

Answer: (b)

Solution

Out of the three types of radiation, UV rays would be having highest frequency. The maximum kinetic energy is $$K_{max} = hf - \phi$$ Clearly, the maximum kinetic energy is dependant on the frequency of the incident radiation and the work function of the metal. From the given spectrums UV rays have the highest energy. Hence, this option is the correct one.

Question 47

Physics · Electric Charges and Fields · Single correct

A 10 $\,$ $\mu$ $\mathrm{C}$ charge is divided into two parts and placed at 1 $\,$ $\mathrm{cm}$ distance so that the repulsive force between them is maximum. The charges of the two parts are:

  1. 7 $\,$ $\mu$ $\mathrm{C}$, 3 $\,$ $\mu$ $\mathrm{C}$
  2. 8 $\,$ $\mu$ $\mathrm{C}$, 2 $\,$ $\mu$ $\mathrm{C}$
  3. 5 $\,$ $\mu$ $\mathrm{C}$, 5 $\,$ $\mu$ $\mathrm{C}$
  4. 9 $\,$ $\mu$ $\mathrm{C}$, 1 $\,$ $\mu$ $\mathrm{C}$

Answer: (c)

Solution

Let the charges be $x \, \mu \mathrm{C}$, $(q - x) \, \mu \mathrm{C}$, where $q = 10 \, \mu \mathrm{C}$. The force between them is $$F = \frac{Kx(q-x)}{r^2}.$$ For the force to be maximum, $$\frac{dF}{dx} = 0$$ $$\Rightarrow \frac{dF}{dx} = \frac{K(q-2x)}{r^2} = 0$$ $$\Rightarrow x = \frac{q}{2} = 5 \, \mu \mathrm{C}$$

Question 48

Physics · Thermodynamics · Single correct

In the equation $\left[X + \dfrac{a}{Y^2}\right]\left[Y - b\right] = RT$, $X$ is pressure, $Y$ is volume, $R$ is universal gas constant and $T$ is temperature. The physical quantity equivalent to the ratio $\dfrac{a}{b}$ is:

  1. Pressure gradient
  2. Energy
  3. Impulse
  4. Coefficient of viscosity

Answer: (b)

Solution

Given $X$ and $\frac{a}{Y^2}$ have the same dimensions. $Y$ and $b$ also have the same dimensions. Therefore, $$\frac{a}{Y^2} = ML^{-1}T^{-2}$$ implies $$a = ML^{-1}T^{-2} \times L^6 = ML^5T^{-2}$$ and $b = L^3$. So, the dimensions of $\frac{a}{b}$ is, $$\frac{a}{b} = \frac{ML^5T^{-2}}{L^3} = ML^2T^{-2}.$$ This is the dimensional form of energy. Hence, this is the right option.

Question 49

Physics · Wave Optics · Single correct

In a Young's double slit experiment, the ratio of amplitude of light coming from slits is 2 : 1. The ratio of the maximum to minimum intensity in the interference pattern is

  1. 9 : 4
  2. 25 : 9
  3. 2 : 1
  4. 9 : 1

Answer: (d)

Solution

The ratio of the maximum to minimum intensity is given by $$\frac{I_{\max}}{I_{\min}} = \left( \frac{\sqrt{I_1} + \sqrt{I_2}}{\sqrt{I_1} - \sqrt{I_2}} \right)^2$$ It is given that $\frac{A_1}{A_2} = \frac{2}{1}$. $$\frac{I_{\max}}{I_{\min}} = \left( \frac{A_1 + A_2}{A_1 - A_2} \right)^2 = \frac{A_2^2 (2 + 1)^2}{A_2^2 (2 - 1)^2} = \left( \frac{2 + 1}{2 - 1} \right)^2 = \frac{9}{1}$$

Question 50

Physics · Kinetic Theory · Single correct

The mean free path of molecules of a certain gas at STP is $1500d$, where $d$ is the diameter of the gas molecules. While maintaining the standard pressure, the mean free path of the molecules at $373 \, K$ is approximately:

  1. $750d$
  2. $1098d$
  3. $2049d$
  4. $1500d$

Answer: (c)

Solution

The mean free path is given by the relation, $$\lambda = \frac{RT}{\sqrt{2} \pi d^2 N_A P}$$ So, $\lambda \propto T$ Let $\lambda'$ be the new mean free path. Hence, $$\frac{1500d}{\lambda'} = \frac{273}{373}$$ $$\Rightarrow \lambda' = 2049.45d \approx 2049d$$

Question 51

Physics · Ray Optics and Optical Instruments · Numerical

A bi convex lens of focal length 10 cm is cut into two identical parts along a plane perpendicular to the principal axis. The power of each lens after cut is

Answer: 5

Solution

The focal length of the bi-convex lens ($f$) can be calculated as follows: $$\frac{1}{f} = (\mu - 1) \left( \frac{1}{R} - \frac{1}{-R} \right)$$ $$= \frac{2(\mu - 1)}{R} \ldots(1)$$ When the lens is cut into two halves, the focal length ($f'$) of each part can be calculated as follows: $$\frac{1}{f'} = (\mu - 1) \left( \frac{1}{R} - \frac{1}{\infty} \right)$$ $$= \frac{(\mu - 1)}{R} \ldots(2)$$ Hence, the ratio of the powers for both the lenses can be given by $$\frac{P'}{P} = \frac{\frac{1}{f'}}{\frac{1}{f}}$$ $$= \frac{f}{f'}$$ $$= \frac{(\mu - 1)}{\frac{R}{2(\mu - 1)}}$$ $$= \frac{1}{2}$$ $$\Rightarrow P' = \frac{P}{2} \ldots(3)$$ Substitute the value of the known parameter into equation (3) to calculate the required power. $$P' = \frac{10}{2}$$ $$= 5 \, \mathrm{D}$$

Question 52

Physics · Atoms · Numerical

An atom absorbs a photon of wavelength 500 nm and emits another photon of wavelength 600 nm. The net energy absorbed by the atom in this process is $n \times 10^{-4}$ eV. The value of $n$ is [Assume the atom to be stationary during the absorption and emission process] (Take $h = 6.6 \times 10^{-34} \, \mathrm{J \, s}$ and $c = 3 \times 10^{8} \, \mathrm{m \, s^{-1}}$).

Answer: 4125

Solution

The energy of a photon is given by $E = \frac{hc}{\lambda}$. It is given that $\lambda_1 = 500 \, \mathrm{nm}$, $\lambda_2 = 600 \, \mathrm{nm}$. The net energy absorbed is $$\Delta E = \frac{hc}{\lambda_1} - \frac{hc}{\lambda_2} = \frac{hc}{10^{-9}} \left( \frac{1}{500} - \frac{1}{600} \right)$$ $$= \frac{6.6 \times 10^{-34} \times 3 \times 10^8 \times 100}{500 \times 600 \times 10^{-9}}$$ $$= \frac{6.6 \times 3}{30} \times 10^{-19} \, \mathrm{J}$$ $$1 \, \mathrm{eV} = 1.6 \times 10^{-19} \, \mathrm{J}$$ $$= \frac{6.6 \times 3}{30 \times 1.6} \, \mathrm{eV}$$ $$= 4125 \times 10^{-4} \, \mathrm{eV}$$

Question 53

Physics · Electric Charges and Fields · Numerical

Three point charges $q$, $-2q$ and $2q$ are placed on $x$ axis at a distance $x = 0$, $x = \frac{3}{4}R$ and $x = R$ respectively from origin as shown. If $q = 2 \times 10^{-6} \, \mathrm{C}$ and $R = 2 \, \mathrm{cm}$, the magnitude of net force experienced by the charge $-2q$ is N.

Answer: 5440

Solution

The net force on the given charge will be the resultant of the forces due to the other two charges. Hence, the net force ($F_n$) can be calculated as follows: $$F_n = \frac{1}{4\pi \varepsilon_0} \frac{4q^2}{\left( \frac{R}{4} \right)^2} - \frac{1}{4\pi \varepsilon_0} \frac{2q^2}{\left( \frac{3R}{4} \right)^2}$$ $$= 9 \times 10^9 \times \frac{16q^2}{R^2} \left[ 4 - \frac{2}{9} \right]$$ $$= 9 \times 10^9 \times \frac{16 \times \left( 2 \times 10^{-6} \, \mathrm{C} \right)^2}{\left( 0.02 \, \mathrm{m} \right)^2} \times \frac{34}{9}$$ $$= 5440 \, \mathrm{N}$$

Question 54

Physics · Electrostatic Potential and Capacitance · Fill in the blank

In the circuit shown, the energy stored in the capacitor is $n \, \mu \mathrm{J}$. The value of $n$ is _____.

Answer: 75

Solution

The capacitor works as an open circuit in the given configuration. The potential difference between the two plates of the capacitor will be the difference across the resistors having resistances $3 \, \Omega$ and $4 \, \Omega$. Hence, the potential difference $(\Delta V)$ across the capacitor can be calculated as follows: $$\Delta V = \left( \frac{4}{6} \times 12 - \frac{3}{12} \times 12 \right) \, \mathrm{V}$$ $$= 5 \, \mathrm{V}$$ The formula to calculate the energy stored in the capacitor is given by $$U = \frac{1}{2} C (\Delta V)^2 \ldots (1)$$ Substitute the values of the known parameters into equation (1) to calculate the required energy stored. $$U = \frac{1}{2} \times 6 \, \mu \mathrm{F} \times (5 \, \mathrm{V})^2$$ $$= 75 \, \mu \mathrm{J}$$

Question 55

Physics · Electromagnetic Induction · Numerical

An insulated copper wire of 100 turns is wrapped around a wooden cylindrical core of the cross-sectional area $24 \, \mathrm{cm}^2$. The two ends of the wire are connected to a resistor. The total resistance in the circuit is $12 \, \Omega$. If an externally applied uniform magnetic field in the core along its axis changes from $1.5 \, \mathrm{T}$ in one direction to $1.5 \, \mathrm{T}$ in the opposite direction, the charge flowing through a point in the circuit during the change of magnetic field will be _____ mC.

Answer: 60

Solution

The induced emf (ε) in the turns of the coil can be written as $$ \varepsilon = - \frac{d\varphi}{dt}$$ $$= iR \ldots (1)$$ Simplify equation (1) to obtain the required charge through a point in the circuit. $$- \frac{d\varphi}{dt} = iR$$ $$\Rightarrow - \frac{1}{R} \int_{\varphi_1}^{\varphi_2} d\varphi = \int idt$$ $$\Rightarrow q = \frac{\varphi_1 - \varphi_2}{R} \ldots (2)$$ Where, $\varphi_1$, $\varphi_2$ are the magnetic flux associated with the coil from two ends. As, $\varphi = NBA$, from equation (2), it can be written that $$q = \frac{NA}{R} \left( B_1 - B_2 \right) \ldots (3)$$ where, $N$, $A$ are the number of turns and the cross-sectional area of the core respectively. Substitute the values of the known parameters into equation (3) to calculate the required charge. $$q = \frac{100 \times 24 \times 10^{-4} \, \mathrm{m^2} \times (1.5 \, \mathrm{T} - (-1.5 \, \mathrm{T}))}{12 \, \Omega}$$ $$= 0.06 \, \mathrm{C} \times \frac{1000 \, \mathrm{mC}}{1 \, \mathrm{C}}$$ $$= 60 \, \mathrm{mC}$$

Question 56

Physics · Waves · Numerical

In an experiment with sonometer when a mass of $180 \, \mathrm{g}$ is attached to the string, it vibrates with fundamental frequency of $30 \, \mathrm{Hz}$. When a mass $m$ is attached, the string vibrates with fundamental frequency of $50 \, \mathrm{Hz}$. The value of $m$ is _______ $\mathrm{g}$.

Answer: 500

Solution

The formula to calculate the fundamental frequency in a stretched string is given by $$f = \frac{1}{2L} \sqrt{\frac{T}{\mu}} \cdots(1)$$ For the first mass, it can be written that $$f_1 = \frac{1}{2L} \sqrt{\frac{m_1 g}{\mu}} \cdots(2)$$ And, for the second mass, it can be written that $$f_2 = \frac{1}{2L} \sqrt{\frac{m_2 g}{\mu}} \cdots(3)$$ Divide equation (3) by equation (2) and simplify to obtain the required mass. $$\frac{f_2}{f_1} = \frac{\frac{1}{2L} \sqrt{\frac{m_2 g}{\mu}}}{\frac{1}{2L} \sqrt{\frac{m_1 g}{\mu}}}$$ $$= \sqrt{\frac{m_2}{m_1}}$$ $$\Rightarrow \frac{m_1}{m_2} = \left(\frac{f_1}{f_2}\right)^2$$ $$\Rightarrow m_2 = m_1 \left(\frac{f_2}{f_1}\right)^2 \cdots(4)$$ Substitute the values of the known parameters into equation (4) to calculate the required mass. $$m_2 = 180 \, \mathrm{g} \times \left(\frac{50 \, \mathrm{Hz}}{30 \, \mathrm{Hz}}\right)^2$$ $$= 500 \, \mathrm{g}$$

Question 57

Physics · System of Particles and Rotational Motion · Numerical

A light rope is wound around a hollow cylinder of mass $5 \, \mathrm{kg}$ and radius $70 \, \mathrm{cm}$. The rope is pulled with a force of $52.5 \, \mathrm{N}$. The angular acceleration of the cylinder will be \, $\mathrm{rad}$ \, $\mathrm{s}^{-2}$

Answer: 15

Solution

The formula to calculate the moment of inertia ($I$) of the cylinder about its radial axis is given by $$I = Mr^2 \ldots (1)$$ Also, the torque ($\tau$) on the cylinder about the central axis because of the application of the external force is given by $$\tau = Fr \ldots (2)$$ Also, the torque can be expressed as $$\tau = I \alpha \ldots (3)$$ Substitute the expressions from equation (1) and (2) into equation (3) and simplify to obtain the angular acceleration. $$Fr = Mr^2 \alpha$$ $$\Rightarrow \alpha = \frac{F}{Mr} \ldots (4)$$ Substitute the values of the known parameters into equation (4) to calculate the required angular acceleration. $$\alpha = \frac{52.5 \, \mathrm{N}}{5 \, \mathrm{kg} \times 0.70 \, \mathrm{m}}$$ $$= 15 \, \mathrm{rad} \, \mathrm{s}^{-2}$$

Question 58

Physics · Work, Energy and Power · Numerical

A car accelerates from rest of $u \, \mathrm{m} \, \mathrm{s}^{-1}$. The energy spent in this process is $E \, \mathrm{J}$. The energy required to accelerate the car from $u \, \mathrm{m} \, \mathrm{s}^{-1}$ to $2u \, \mathrm{m} \, \mathrm{s}^{-1}$ is $nE \, \mathrm{J}$. The value of $n$ is _____.

Answer: 3

Solution

The kinetic energy of a moving particle is given by $$E = \frac{1}{2} mu^2 \cdots (1)$$ When the final velocity of the particle becomes twice the initial velocity, the kinetic energy of the particle can be written as $$nE = \frac{1}{2} m \left\{ (2u)^2 - u^2 \right\}$$ $$= \frac{1}{2} m (3u^2) \cdots (2)$$ Divide equation (2) by equation (1) and solve to calculate the value of $n$. $$\frac{nE}{E} = \frac{\frac{1}{2} m (3u^2)}{\frac{1}{2} mu^2}$$ $$\Rightarrow n = 3$$

Question 59

Physics · Thermal Properties of Matter · Numerical

Two plates A and B have thermal conductivities $84 \, \mathrm{W \, m^{-1} \, K^{-1}}$ and $126 \, \mathrm{W \, m^{-1} \, K^{-1}}$ respectively. They have same surface area and same thickness. They are placed in contact along their surfaces. If the temperatures of the outer surfaces of A and B are kept at $100^\circ \mathrm{C}$ and $0^\circ \mathrm{C}$ respectively, then the temperature of the surface of contact in steady state is _____ $^\circ \mathrm{C}$.

Answer: 40

Solution

Let the temperature of the contact surface be $T$. So, $H_A = H_B$. $$\frac{K_A A'(T_A - T)}{L} = \frac{K_B A'(T - T_B)}{L}$$ $$\Rightarrow 84(100 - T) = 126(T - 0)$$ $$\Rightarrow 2(100 - T) = 3T$$ $$\Rightarrow T = 40 \, ^\circ \mathrm{C}$$

Question 60

Physics · Moving Charges and Magnetism · Numerical

A straight wire AB of mass 40 g and length 50 cm is suspended by a pair of flexible leads in a uniform magnetic field of magnitude 0.40 T as shown in the figure. The magnitude of the current required in the wire to remove the tension in the supporting leads is _____ A. (Take g = 10 m s$^{-2}$).

Answer: 2

Solution

The formula to calculate the magnetic force on the conductor is given by $$F_B = ILB \ldots (1)$$ The formula to calculate the gravitational force on the conductor is given by $$F_G = mg \ldots (2)$$ Equate both the equations and simplify to obtain the required current through the conductor. $$ILB = mg$$ $$\Rightarrow I = \frac{mg}{LB} \ldots (3)$$ Substitute the values of the known parameters into equation (3) to calculate the required current through the conductor. $$I = \frac{\frac{40}{1000} \, \mathrm{kg} \times 10 \, \mathrm{m \, s^{-2}}}{0.5 \, \mathrm{m} \times 0.40 \, \mathrm{T}}$$ $$= 2 \, \mathrm{A}$$

Chemistry

Question 61

Chemistry · Analytical Chemistry · Single correct

In the wet tests for detection of various cations by precipitation, $Ba^{2+}$ cations are detected by obtaining precipitate of

  1. Ba(ox) : Barium oxalate
  2. BaCO$_3$
  3. Ba(OAc)$_2$
  4. BaSO$_4$

Answer: (b)

Solution

Ba^{2+} belongs to V^{th} Group and hence they are precipitated with CO_3^{2-} to give ppt of BaCO_3. In Wet tests for cations, (NH_4)_2 CO_3 is used as a group reagent for fifth group cations $\left$( Ba^{2+}, Ca^{2+}, Sr^{2+} $\right$). $$Ba^{2+} + \left( NH_4 \right)_2 CO_3 \rightarrow BaCO_3 + NH_4^+$$

Question 62

Chemistry · Biomolecules · Single correct

The naturally occurring amino acid that contains only one basic functional group in its chemical structure is

  1. asparagine
  2. histidine
  3. arginine
  4. lysine

Answer: (a)

Solution

Asparagine have only one basic functional Group Structure of Asparagine: There are three amino acids that have basic side chains at neutral pH. These are arginine (Arg), lysine (Lys), and histidine (His). Their side chains contain nitrogen and resemble ammonia, which is a base. Their pKa's are high enough that they tend to bind protons, gaining a positive charge in the process.

Question 63

Chemistry · General Principles and Processes of Isolation of Elements · Single correct

Given below are two statements related to Ellingham diagram: Statement I: Ellingham diagrams can be constructed for formation of oxides, sulphides and halides of metals. Statement II: It consists of plots of $\Delta H^\circ$ vs $T$ for formation of oxides of elements. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both Statement I and Statement II are correct
  2. Both Statement I and Statement II are incorrect
  3. Statement I is correct but Statement II is incorrect
  4. Statement I is incorrect but Statement II is correct

Answer: (c)

Solution

An Ellingham diagram is a graph showing the temperature dependence of the stability of compounds. Ellingham diagrams can be drawn for Sulphides, Oxides and Halides. The Ellingham diagram is a graph that shows how the $\Delta G_f^0$ varies with temperature as a result of the formation of elemental oxides.

Question 64

Chemistry · Surface Chemistry · Single correct

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : The diameter of colloidal particles in solution should not be much smaller than wavelength of light to show Tyndall effect. Reason R : The light scatters in all directions when the size of particles is large enough. In the light of the above statements, choose the correct answer from the options given below :

  1. Both A and R are correct but R is NOT the correct explanation of A
  2. A is true but R is false
  3. A is false but R is true
  4. Both A and R are correct and R is the correct explanation of A

Answer: (d)

Solution

Conditions for Tyndall effect: (i) Diameter of colloidal particles in solution is not much smaller than wavelength of the light used. (ii) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude. If size of particles is large enough then light scatters in all directions. So Both A and R are correct and R is the correct explanation of A.

Question 65

Chemistry · Co-ordination Compounds · Single correct

The total number of stereoisomers for the complex $[\mathrm{Cr}(\mathrm{ox})_2 \mathrm{ClBr}]^{3-}$ (where ox = oxalate) is

  1. 3
  2. 2
  3. 4
  4. 1

Answer: (a)

Solution

The complex $[\mathrm{Cr(ox)_2ClBr}]^{3-}$ exhibits two geometrical isomers. Among these isomers, the cis-isomer is optically active. Hence, the total number of stereoisomers for the given complex is 3.

Question 66

Chemistry · The p-Block Elements (Group 15, 16, 17 & 18) · Single correct

Better method for preparation of $\mathrm{BeF_2}$, among the following is

  1. $\mathrm{BeO + C + F_2 \xrightarrow{\Delta}}$ $BeF_2$
  2. $\mathrm{(NH_4)_2 BeF_4 \xrightarrow{\Delta}}$ $BeF_2$
  3. $\mathrm{Be + F_2 \xrightarrow{\Delta}}$ $BeF_2$
  4. $\mathrm{BeH_2 + F_2 \xrightarrow{\Delta}}$ $BeF_2$

Answer: (b)

Solution

The beryllium fluoride cannot be easily prepared by simple methods. It is known that beryllium oxide dissolves in aqueous hydrofluoric acid with the formation of the fluoride, but on evaporation of the resulting solution some of the combined acid is lost, and the residue is believed to be an oxy fluoride. Thermal decomposition of $(\mathrm{NH_4})_2 \mathrm{BeF_4}$ is the best route for the preparation of $\mathrm{BeF_2}$. $$(\mathrm{NH_4})_2 \mathrm{BeF_4} \rightarrow 2 \mathrm{NH_4} \mathrm{F} + \mathrm{BeF_2}$$

Question 67

Chemistry · Hydrogen · Single correct

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Isotopes of hydrogen have almost same chemical properties, but difference in their rates of reactions. Reason R: Isotopes of hydrogen have different enthalpy of bond dissociation. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both A and R are correct but R is NOT the correct explanation of A
  2. Both A and R are correct and R is the correct explanation of A
  3. A is not correct but R is correct
  4. A is correct but R is not correct

Answer: (b)

Solution

While isotopes of an element have the same electronic configuration, their chemical properties can differ slightly due to differences in their atomic mass. Isotopes of an element have the same number of protons but varying numbers of neutrons, which affects the overall mass of the atom. The only difference is in their rates of reactions, mainly due to their different enthalpy of bond dissociation.

Question 68

Chemistry · Organic Chemistry — Some Basic Principles & Techniques · Single correct

Given below are two statements: Statement I: Tropolone is an aromatic compound and has $8\pi$ electrons. Statement II: $\pi$ electrons of $>\mathrm{C} = \mathrm{O}$ group in tropolone is involved in aromaticity. In the light of the above statements choose the correct answer from the options given below:

  1. Statement I is true but Statement II is false
  2. Statement I is false but Statement II is true
  3. Both Statement I and Statement II are false
  4. Both Statement I and Statement II are true

Answer: (a)

Solution

Tropolone is an aromatic compound and has $8\pi e^-$ electrons ($6\pi e^-$ are endocyclic and $2\pi e^-$ are exocyclic) and $\pi$ electrons of $> \mathrm{C} = \mathrm{O}$ group in tropolone is not involved in aromaticity.

Question 69

Chemistry · Amines · Single correct

Compound A from the following reaction sequence is:

  1. Benzoic Acid
  2. Aniline
  3. Salicylic Acid
  4. Phenol

Answer: (d)

Solution

When aniline treated with bromine, the reaction results in the formation of 2, 4, 6-tribromo phenylamine. This reaction is an example of bromination. The process of conversion of a primary aromatic amino compound into a diazonium salt is known as diazotization. This process is carried out by adding an aqueous solution of sodium nitrite to a solution of primary aromatic amine (e.g., aniline) in excess of HCl at a temperature below $5^\circ \mathrm{C}$. Benzene diazonium chloride reacts with $\mathrm{H_3PO_2}$ in aqueous medium to form benzene.

Question 70

Chemistry · Organic Chemistry — Some Basic Principles & Techniques · Single correct

The major product for the following reaction is:

Answer: (b)

Solution

Nucleophilicity of sulfur-containing nucleophiles (such as $\mathrm{SH}^-$) is higher than that of oxygen-containing nucleophiles (such as $\mathrm{OH}^-$). Here sulfur containing nucleophile can donate its lone pair. A stable carbocation is formed next, stable carbocation will be that which is away from CN group.

Question 71

Chemistry · Environmental Chemistry · Single correct

Which of the following are the Green house gases? A. Water vapour B. Ozone C. $\mathrm{I}_2$ D. Molecular hydrogen Choose the most appropriate answer from the options given below :

  1. A and D only
  2. B and C only
  3. A and B only
  4. C and D only

Answer: (c)

Solution

The greenhouse effect is a process that occurs when gases in Earth's atmosphere trap the Sun's heat. This process makes Earth much warmer than it would be without an atmosphere. The main greenhouse gases whose concentrations are rising are carbon dioxide, methane, nitrous oxide, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and ozone in the lower atmosphere. $\mathrm{I_2}$ and $\mathrm{H_2}$ are not greenhouse gases.

Question 72

Chemistry · Polymers · Single correct

Match List-I with List-II. Choose the correct answer from the options given below

  1. A-IV, B-II, C-III, D-I
  2. A-IV, B-I, C-III, D-II
  3. A-II, B-IV, C-I, D-III
  4. A-III, B-I, C-IV, D-II

Answer: (d)

Solution

(A) Weak intermolecular forces are present in polymer of 2-chloro, 1, 3-butadiene. It is a monomer of neoprene which is a rubber (elastomer). (B) Hydrogen bonding is present in NYLON-6, 6 which is a polymer of hexamethylenediamine and adipic acid. This hydrogen bonding is due to the presence of amide group. (C) Heavily branched polymer is Bakelite which is polymer of phenol and formaldehyde. It is a crosslinked polymer. (D) High density polymer (polyethylene) preparation requires $\mathrm{Al(Et)_3}$ and $\mathrm{TiCl_4}$ as a catalyst (Ziegler Natta Catalyst).

Question 73

Chemistry · Chemical Bonding and Molecular Structure · Single correct

Given below are two statements: Statement I: $SO_2$ and $H_2O$ both possess V-shaped structure Statement II: The bond angle of $SO_2$ is less than that of $H_2O$. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both Statement I and Statement II are incorrect
  2. Both Statement I and Statement II are correct
  3. Statement I is incorrect but Statement II is correct
  4. Statement I is correct but Statement II is incorrect

Answer: (d)

Solution

The molecule $\mathrm{SO_2}$ is having two sigma bond pairs and lone pair, hence, it exhibits angular or V-shape structure. The molecule $\mathrm{H_2O}$ is having two sigma bond pairs and a lone pair hence, it exhibits angular or V-shape structure. So, both molecules are having same shape. But double bond-double bond repulsions are greater than single bond repulsions, hence, the bond angle in sulphur dioxide is greater than water. $\mathrm{SO_2}$ and $\mathrm{H_2O}$ both have V-Shape Bond angle: $\mathrm{SO_2} > \mathrm{H_2O}$

Question 74

Chemistry · The p-Block Elements (Group 15, 16, 17 & 18) · Single correct

The correct group of halide ions which can be oxidised by oxygen in acidic medium is

  1. $\mathrm{Br}^-$ and $\mathrm{I}^-$ only
  2. $\mathrm{Br}^-$ only
  3. $\mathrm{I}^-$ only
  4. $\mathrm{Cl}^-$, $\mathrm{Br}^-$ and $\mathrm{I}^-$ only

Answer: (c)

Solution

Fluorine oxidises water to oxygen whereas chlorine and bromine react with water to form corresponding HX and HOX acids. $$2\mathrm{F_2} + 2\mathrm{H_2O} \rightarrow 4\mathrm{HF} + \mathrm{O_2}$$ $$\mathrm{Cl_2} + \mathrm{H_2O} \rightarrow \mathrm{HCl} + \mathrm{HOCl}$$ The reaction of $\mathrm{I_2}$ with water is nonspontaneous. In fact, $\mathrm{I^-}$ can be oxidised by oxygen in acidic medium. It is why the $\mathrm{I^-}$ in nature is not present in that much amount as other halides are present in nature.

Question 75

Chemistry · Hydrocarbons · Single correct

What happens when methane undergoes combustion in systems A and B respectively?

  1. System A: Temperature rises, System B: Temperature remains same
  2. System A: Temperature remains same, System B: Temperature rises
  3. System A: Temperature falls, System B: Temperature remains same
  4. System A: Temperature falls, System B: Temperature rises

Answer: (a)

Solution

For an adiabatic free expansion of an ideal gas, the gas is kept in an insulated container and then permitted to enlarge in a vacuum. Since there is no external pressure for the gas to enlarge against, the work done by or on the system is zero. Since this process does not involve any exchange of heat transfer or work, heat will not escape and temperature of system will rise. For diathermic container, heat will escape the container and hence temperature of container will remain same.

Question 76

Chemistry · Organic Chemistry — Some Basic Principles & Techniques · Single correct

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Order of acidic nature of the following compounds is $A > B > C$. Reason R: Fluoro is a stronger electron withdrawing group than Chloro group. In the light of the above statements, choose the correct answer from the options given below :

  1. A is false but R is true
  2. Both A and R are correct and R is the correct explanation of A
  3. A is true but R is false
  4. Both A and R are correct but R is NOT the correct explanation of A

Answer: (d)

Solution

The electron withdrawing groups decrease the acidic nature and the electron releasing groups increase the acidic nature. The F and Cl are electron withdrawing while CH_3 is electron releasing, hence acidic strength will be $$O - H Cl > OH F > OH CH_3$$ On further differentiation, the $-I$ effect depends most importantly on distance, hence. $$OH Cl > OH F > OH CH_3$$ The F has a higher $-I$ effect compared to Cl, hence the reason is a correct statement, but the $-I$ effect depends more on distance as compared to power, hence $$OH Cl$$ is stronger acid than $$OH F$$

Question 77

Chemistry · Classification of Elements and Periodicity in Properties · Single correct

Identify the correct order of standard enthalpy of formation of sodium halides.

  1. $\mathrm{NaI} < \mathrm{NaBr} < \mathrm{NaF} < \mathrm{NaCl}$
  2. $\mathrm{NaI} < \mathrm{NaBr} < \mathrm{NaCl} < \mathrm{NaF}$
  3. $\mathrm{NaF} < \mathrm{NaCl} < \mathrm{NaBr} < \mathrm{NaI}$
  4. $\mathrm{NaCl} < \mathrm{NaF} < \mathrm{NaBr} < \mathrm{NaI}$

Answer: (b)

Solution

The lattice energy of an ionic compound is the energy required to separate one mole of the compound into its constituent ions in the gas phase. Lattice energy $\propto \frac{1}{(r_+ + r_-)}$ The lattice energy is inversely proportional to the sum of the ionic radii $(r_+ + r_-)$ of the ions involved. When the size of the ions increases, the distance between them also increases, leading to a decrease in the attractive forces between the ions and a decrease in the lattice energy. Therefore, if the size of the ions increases, the lattice energy generally decreases. So Order: $\mathrm{NaF} > \mathrm{NaCl} > \mathrm{NaBr} > \mathrm{NaI}$

Question 78

Chemistry · Haloalkanes and Haloarenes · Single correct

Match List-I with List-II. 1-Bromopropane is reacted with reagents in List-I to give product in List-II Choose the correct answer from the options given below

  1. A-III, B-I, C-IV, D-II
  2. A-I, B-II, C-III, D-IV
  3. A-I, B-III, C-IV, D-II
  4. A-IV, B-III, C-II, D-I

Answer: (a)

Solution

(A) When 1-bromopropane reacts with alcoholic KOH, the bromine with the alpha H (hydrogen from the carbon alongside the carbon fortified with useful gathering) is eliminated and subsequently forms 1-propene. $$CH_2 - CH_2 - CH_3 \xrightarrow{Alc. KOH} CH_2 = CH - CH_3$$ (B) When 1-bromo propane reacts with alc KCN it will form butanenitrile. $$\begin{array}{c} CH_2 - CH_2 - CH_3 \\ | \\ Br \end{array} \xrightarrow{KCN} \begin{array}{c} CH_2 - CH_2 - CH_3 \\ | \\ C \equiv N (nitrile) \end{array}$$ (C) When alkyl halide reacts with silver nitrite, nitroalkane is formed because the bond between Ag - OAg - O is covalent, the lone pair on nitrogen acts as an attacking site for nucleophilic substitution. $$\begin{array}{c} CH_2 - CH_2 - CH_3 \\ | \\ Br \end{array} \xrightarrow{AgNO_2} \begin{array}{c} CH_2 - CH_2 - CH_3 \\ | \\ NO_2 (Nitroalkane) \end{array}$$ (D) When 1-bromopropane reacts with silver acetate, propyl ethanoate and silver bromide are formed. $$\begin{array}{c} CH_2 - CH_2 - CH_3 \\ | \\ Br \end{array} \xrightarrow{CH_3COOAg} \begin{array}{c} CH_2 - CH_2 - CH_3 \\ | \\ O - C - CH_3 \\ || \\ O (ester) \end{array}$$

Question 79

Chemistry · Co-ordination Compounds · Single correct

The covalency and oxidation state respectively of boron in $[\mathrm{BF}_4]^-$, are

  1. 3 and 5
  2. 3 and 4
  3. 4 and 4
  4. 4 and 3

Answer: (d)

Solution

Number of covalent bonds formed by Boron is 4. $[\mathrm{BF}_4]^-$ Covalency = 4. The oxidation state of an element represents the charge it would have if all the bonding electrons were assigned to the more electronegative atom in the bond. Oxidation number of fluorine is $-1$. Then, $$\mathrm{B} + 4 \times (-1) = -1$$ $$\mathrm{B} - 4 = -1$$ $$\mathrm{B} = +3$$ Oxidation state = $+3$ for Boron.

Question 80

Chemistry · Co-ordination Compounds · Single correct

Which of the following complexes will exhibit maximum attraction to an applied magnetic field?

  1. $[\mathrm{Ni(H_2O)_6}]^{2+}$
  2. $[\mathrm{Co(en)_3}]^{3+}$
  3. $[\mathrm{Zn(H_2O)_6}]^{2+}$
  4. $[\mathrm{Co(H_2O)_6}]^{2+}$

Answer: (d)

Solution

Complex having maximum number of unpaired electrons will exhibit maximum attraction to applied magnetic field. $$[\mathrm{Zn} (\mathrm{H}_2\mathrm{O})_6]^{2+} \rightarrow d^{10} system, t_{2g}^6 e_g^4, 0 unpaired electrons$$ $$[\mathrm{Co} (\mathrm{H}_2\mathrm{O})_6]^{2+} \rightarrow d^7 system, t_{2g}^5 e_g^2, 3 unpaired electrons$$ $$[\mathrm{Co(en)}_3]^{3+} \rightarrow d^6 system, t_{2g}^6 e_g^0, 0 unpaired electrons$$ $$[\mathrm{Ni} (\mathrm{H}_2\mathrm{O})_6]^{2+} \rightarrow d^8 system, t_{2g}^6 e_g^2, 2 unpaired electrons.$$ So Option D is correct.

Question 81

Chemistry · Organic Chemistry — Some Basic Principles & Techniques · Numerical

0.400 $\mathrm{g}$ of an organic compound (X) gave 0.376 $\mathrm{g}$ of $\mathrm{AgBr}$ in Carius method for estimation of bromine. $\%$ of bromine in the compound (X) is (Given: Molar mass $\mathrm{AgBr}$ = 188 $\mathrm{g}$ $\mathrm{mol}^{-1}$ , $\mathrm{Br}$ = 80 $\mathrm{g}$ $\mathrm{mol}^{-1})$

Answer: 40

Solution

The percentage composition of element is given by the formula: $$\frac{mass of element}{mass of organic compound} \times 100$$ Moles of AgBr is given by $$\frac{0.376}{188}$$ Moles of Br is also $$\frac{0.376}{188}$$ Mass of Br is $$\frac{0.376}{188} \times 80$$ The percentage of Br is $$\frac{0.376 \times 80}{188 \times (0.400)} \times 100$$ which equals $$40\%$$

Question 82

Chemistry · Some Basic Concepts of Chemistry · Numerical

$1 \, \mathrm{g}$ of a carbonate ($M_2\mathrm{CO}_3$) on treatment with excess HCl produces $0.01 \, \mathrm{mol}$ of $\mathrm{CO}_2$. The molar mass of $M_2\mathrm{CO}_3$ is _______ $\mathrm{g \, mol^{-1}}$. (Nearest integer)

Answer: 100

Solution

From the balanced chemical reaction, $\mathrm{M_2CO_3 + 2HCl \rightarrow 2MCl + H_2O + CO_2}$. Here from this, we get: $0.01 \, \mathrm{mol} \, \mathrm{CO_2} \equiv 0.01 \, \mathrm{mol} \, \mathrm{M_2CO_3} \equiv 1 \, \mathrm{g} \, \mathrm{M_2CO_3}$. We know that, number of moles $= \frac{\text{Given mass}}{\text{Molar mass}}$. Therefore, $$\text{Molar mass of } \mathrm{M_2CO_3} = \frac{\text{Given mass of } \mathrm{M_2CO_3}}{\text{Number of Moles of } \mathrm{M_2CO_3}} = \frac{1}{0.01} = 100 \, \mathrm{g/mol}$$

Question 83

Chemistry · Redox Reactions · Numerical

See the following chemical reaction: $Cr_2O_7^{2-}$ + $XH^{+}$ + 6$Fe^{2+}$ $\rightarrow$ $YCr^{3+}$ + 6$Fe^{3+}$ + $ZH_2O$ The sum of X, Y and Z is

Answer: 23

Solution

The given equation can be balanced using ion-electron method as shown below. $\mathrm{Fe^{2+} \rightarrow Fe^{3+} + e^-}$ - oxidation Half reaction $6e^- + 14\mathrm{H^+} + \mathrm{Cr_2 O_7^{2-} \rightarrow 2Cr^{3+} + 7H_2O}$ - Reduction Half reaction The overall reaction is $$6\mathrm{Fe^{2+} + 14H^+ + Cr_2 O_7^{2-} \rightarrow 6Fe^{3+} + 2Cr^{3+} + 7H_2O}$$ The values $X = 14$, $Y = 2$ and $Z = 7$ $(X + Y + Z) = 14 + 2 + 7$ $= 23$

Question 84

Chemistry · The p-Block Elements (Group-13 and 14) · Numerical

If the formula of Borax is $\mathrm{Na}_2 \mathrm{B}_4 \mathrm{O}_x (\mathrm{OH})_y \cdot z\mathrm{H}_2\mathrm{O}$, then $x + y + z =$

Answer: 17

Solution

The crude name of borax is Tincal. It has the molecular formula $\mathrm{Na_2B_4O_7} \cdot 10\mathrm{H_2O}$ and structural formula of borax is $\mathrm{Na_2[B_4O_5(OH)_4] \cdot 8H_2O}$. Based on the structural formula, $x = 5$, $y = 4$ and $z = 8$. $$(x + y + z) = 5 + 4 + 8 = 17$$

Question 85

Chemistry · Electrochemistry · Numerical

At $298\,\mathrm{K}$, the standard reduction potential for the $\mathrm{Cu^{2+}/Cu}$ electrode is $0.34\,\mathrm{V}$. Given: $K_{\mathrm{sp}}\!\left(\mathrm{Cu(OH)_2}\right)=1\times10^{-20}$ Take: $\dfrac{2.303\,RT}{F}=0.059\,\mathrm{V}$ The reduction potential at $\mathrm{pH}=14$ for the above couple is $(-)\,x\times10^{-2}\,\mathrm{V}$. The value of $x$ is:

Answer: 25

Solution

For the reaction: $\mathrm{Cu^{2+}(aq)+2e^- \rightarrow Cu(s)}$ The reduction potential is $E=E^\circ-\dfrac{RT}{2F}\ln\!\left(\dfrac{1}{[\mathrm{Cu^{2+}}]}\right)$ From the given data, $\mathrm{pH}=14$ and $K_{sp}\!\left(\mathrm{Cu(OH)_2}\right)=1.0\times10^{-20}$, we get $[\mathrm{H^+}]=10^{-14}\,\mathrm{M}$ $[\mathrm{OH^-}]=\dfrac{K_w}{[\mathrm{H^+}]} =\dfrac{10^{-14}\,\mathrm{M^2}}{10^{-14}\,\mathrm{M}} =1\,\mathrm{M}$ $[\mathrm{Cu^{2+}}] =\dfrac{K_{sp}}{[\mathrm{OH^-}]^2} =\dfrac{1.0\times10^{-20}\,\mathrm{M^2}}{(1\,\mathrm{M})^2} =1.0\times10^{-20}\,\mathrm{M}$ $E=0.34\,\mathrm{V} -\left(\dfrac{0.059\,\mathrm{V}}{2}\right) \log\!\left(\dfrac{1}{1.0\times10^{-20}}\right)$ $=0.34\,\mathrm{V} -\dfrac{0.059\times20\,\mathrm{V}}{2}$ $E=0.34-0.59$ $=-0.25\,\mathrm{V}$

Question 86

Chemistry · Equilibrium · Numerical

20 $\mathrm{mL}$ of 0.1 $\mathrm{M}$ NaOH is added to 50 $\mathrm{mL}$ of 0.1 $\mathrm{M}$ acetic acid solution. The pH of the resulting solution is $\times$ $10^{-2}$. (Nearest integer) Given: $pK_a$($\mathrm{CH}_3\mathrm{COOH}$) = 4.76 $\log$ 2 = 0.30 $\log$ 3 = 0.48

Answer: 458

Solution

When a strong base is added to a weak acid solution, it results in the formation of a salt. Here, acid is present in a limiting reagent and base is present in excess amounts. So, by using the pH formula: $$pH = pK_a + \log \left( \frac{[salt]}{[acid]} \right)$$ $$CH_3 COOH + NaOH \longrightarrow CH_3 COONa + H_2 O$$ $$\begin{array}{cccc} 5 & 2 & & \\ 3 & 0 & 2 & \\ \end{array}$$ $$pH = pK_a + \log \left( \frac{2}{3} \right)$$ $$pH = 4.76 + 0.30 - 0.48$$ $$= 4.76 - .18$$ $$= 4.58$$

Question 87

Chemistry · Chemical Kinetics and Nuclear Chemistry · Numerical

A(g) $\rightarrow$ 2 \, B(g) + C(g) is a first order reaction. The initial pressure of the system was found to be 800 \, $\mathrm{mm}$ $\;$ $\mathrm{Hg}$ which increased to 1600 \, $\mathrm{mm}$ $\;$ $\mathrm{Hg}$ after 10 \, $\mathrm{min}$. The total pressure of the system after 30 \, $\mathrm{min}$ will be ____$\;$ $\mathrm{mm}$ $\;$ $\mathrm{Hg}$. (Nearest integer)

Answer: 2200

Solution

The final pressure of each component can be calculated as follows. $$\mathrm{A(g)} \rightarrow 2\, \mathrm{B(g)} + \mathrm{C(g)}$$ Initial: $800 0 0$ At time $t$: $800 - p 2p p$ $$800 + 2p = 1600$$ $$2p = 800$$ $$p = 400$$ The first order reaction rate constant can be calculated as follows. $$K = \frac{2.303}{10} \log \frac{800}{400} = \frac{2.303 \times \log 2}{10}$$ For 30 min, $$K = \frac{2.303}{30} \log \frac{(800)}{(800-y)}$$ $$\frac{2.303 \times \log 2}{10} = \frac{2.303}{30} \log \left( \frac{800}{800-y} \right)$$ $$\Rightarrow \left( \frac{800}{800-y} \right) = 8$$ $$100 = 800 - y$$ $$y = 700$$ Total pressure after 30 min: $$(800 - y) + (2y) + (y)$$ $$= 800 + 2y$$ $$= 800 + 1400$$ $$= 2200 \, \mathrm{mm \, Hg}$$

Question 88

Chemistry · Structure of Atom · Numerical

The orbital angular momentum of an electron in 3 s orbital is $\frac{x h}{2 \pi}$. The value of $x$ is (nearest integer)

Answer: 0

Solution

The orbital angular momentum is given by $$\frac{h}{2\pi} \sqrt{l(l+1)}$$ For 3s-electron, $l = 0$. Therefore, the orbital angular momentum is $$\frac{h}{2\pi} \sqrt{0(0+1)}$$ which equals $0$ (zero).

Question 89

Chemistry · The Solid State · Numerical

Sodium metal crystallises in a body-centred cubic lattice with unit cell edge length of $4\,\mathrm{\AA}$. The radius of sodium atom is $\_\_\_ \times 10^{-1}\,\mathrm{\AA}$. (Nearest integer)

Answer: 17

Solution

Edge length of the unit cell ($a$) $= 4 \times 10^{-8} \, \mathrm{cm}$ Radius of sodium atom ($r$) = ? Since, sodium crystallises in body centered cubic arrangement. The radius of the atom and the edge length of the cubic unit cell are related as follows, For bcc structure, $4r = \sqrt{3}a \Rightarrow r = \frac{\sqrt{3}}{4} a$ $$r = \frac{1.732 \times 4 \times 10^{-8}}{4}$$ $$r = 1.732 \times 10^{-8} \, \mathrm{cm}$$ $$r = 17.3 \, \mathrm{\AA}$$

Question 90

Chemistry · Solutions · Numerical

Sea water contains $29.25\%$ $\mathrm{NaCl}$ and $19\%$ $\mathrm{MgCl_2}$ by weight of solution. The normal boiling point of the sea water is $\_\_\_\_$ $^\circ\mathrm{C}$ (Nearest integer). Assume $100\%$ ionization for both $\mathrm{NaCl}$ and $\mathrm{MgCl_2}$. Given: $K_b(\mathrm{H_2O} = 0.52\,\mathrm{K\,kg\,mol^{-1}})$ Molar masses of $\mathrm{NaCl}$ and $\mathrm{MgCl_2}$ are $58.5$ and $95\,\mathrm{g\,mol^{-1}}$, respectively.

Answer: 116

Solution

Molality of solution = $\frac{moles of solute}{mass of solvent}$ $\times$ 1000. Number of moles NaCl = $\frac{29.25}{58.5}$ = 0.5. Number of moles of MgCl_2 = $\frac{19}{95}$ = 0.2. NaCl = $\frac{0.5}{51.75}$ $\times$ 1000. MgCl_2 = $\frac{0.2}{51.75}$ $\times$ 1000. ($\Delta$ T_b) = $\{$(i_1 $\,$ m_1) + (i_2 $\,$ m_2)$\}$ k_b. $\Delta$ T_b = Elevation in boiling point. i = Van't Hoff factor. m = molality. k_b = molal elevation constant. $$\Delta T_b = \left(\frac{2 \times 0.5 \times 1000}{51.75} \times \frac{3 \times 0.2 \times 1000}{51.75}\right) \times 0.52$$ $$= 16.077$$ Boiling point of sea water = 116.077^$\circ$ C $\approx$ 116^$\circ$ C (Nearest integer)