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
The coefficient of $x^5$ in the expansion of $\left(2x^3 - \frac{1}{3x^2}\right)^5$ is
$\frac{80}{9}$
9
8
$\frac{26}{3}$
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
$(-2, 5, 0)$
$(1, -2, 1)$
$(2, 0, 1)$
$(0, 5, -2)$
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
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
3
3$\sqrt{3}$
2
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
$x^2 - 7x + 12 = 0$
$x^2 - 14x + 48 = 0$
$x^2 - 13x + 42 = 0$
$x^2 - 10x + 25 = 0$
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 $\underline{\hspace{2cm}}$.
441
482
841
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
8
6
9
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
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
7
5
6
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
327
328
324
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
$[0, 2\pi]$
$[0, \pi]$
$[0, 2\pi]$
$[0, \pi]$
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
$(\sim p) \lor q$
$(\sim p) \lor (\sim q)$
$p \lor (\sim q)$
$p \lor q$
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
15
11
12
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
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
$\frac{5}{2}$
4
$\frac{7}{2}$
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
$\frac{4}{3} (4\sqrt{2} - 1)$
$\frac{4}{3} (4\sqrt{2} + 1)$
$\frac{3}{4} (4\sqrt{2} + 1)$
$\frac{3}{4} (4\sqrt{2} - 1)$
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
60
54
108
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
$\frac{x+1}{-1} = \frac{y-2}{2} = \frac{z-5}{4}$
$\frac{x+1}{-1} = \frac{y-2}{2} = \frac{z-5}{5}$
$\frac{x-1}{-1} = \frac{y-2}{2} = \frac{z-5}{5}$
$\frac{x+1}{1} = \frac{y-2}{2} = \frac{z-5}{5}$
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 \[ \frac{e^{\frac{\pi}{4}} + \int_{0}^{\pi} e^{-x} \tan^{50} x \, dx}{\int_{0}^{\pi} e^{-x} \left( \tan^{49} x + \tan^{51} x \right) \, dx} \]
51
50
25
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 ______.
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, $\($ E = 1 + 1 + 1 + 2 + 2 + 2 + 2 + 2 + 3 + 3 + 3 + 3 + 3 + 3 + 4 + 4 + $\ldots$ $\)$ $\($ $\Rightarrow$ E = 3 $\times$ 1 + 5 $\times$ 2 + 7 $\times$ 3 + $\ldots$ + 19 $\times$ 9 + 10 $\times$ 21 $\)$ $\($ $\Rightarrow$ E = $\sum$_{r=1}^{10} (2r + 1)r $\)$ $\($ $\Rightarrow$ E = 2 $\sum$_{r=1}^{10} (r^2 + r) $\)$ $\($ $\Rightarrow$ E = 2 $\left$[ $\frac{10 \times 11 \times 21}{6}$ $\right$] + $\frac{10 \times 11}{2}$ $\)$ $\($ $\Rightarrow$ E = 770 + 55 $\)$ $\($ $\Rightarrow$ E = 825 $\)$
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
30
36
42
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
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
A is false but R is true
Both A and R are true and R is the correct explanation of A
Both A and R are true but R is NOT the correct explanation of A
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:
10.3 $\mu$ $\mathrm{C}$
4.8 $\mu$ $\mathrm{C}$
12 $\mu$ $\mathrm{C}$
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
Statement I is incorrect but Statement II is correct
Statement I is correct but statement II is incorrect
Both Statement I and Statement II are incorrect
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:
$\frac{1}{\sqrt{2}} A$
$\frac{2A}{2}$
$\sqrt{2} A$
$\frac{1}{2} A$
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:
120 $\mathrm{m}$
320 $\mathrm{m}$
80 $\mathrm{m}$
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.)
$P_0(4)^\gamma$
$4P_0$
$P_0$
$P_0 \left( 4 \right)^{\frac{1}{\gamma}}$
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
Both A and R are true and R is the correct explanation of A
Both A and R are true but R is NOT the correct explanation of A
A is true but R is false
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:
positive z-axis
positive y-axis
at $45^\circ$ angle from positive $y$-axis
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:
$25 \, \mathrm{m \, s^{-1}}$
$5 \, \mathrm{m \, s^{-1}}$
$62.5 \, \mathrm{m \, s^{-1}}$
$12.5 \, \mathrm{m \, s^{-1}}$
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
A and E only
C and D only
B and E only
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:
2 : 3
2 : 1
3 : 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:
Statement I is false but statement II is true
Statement I is true but statement II is false
Both Statement I and Statement II are false
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:
560 N
2800 N
2240 N
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:
$2\lambda$
$\frac{\lambda}{2}$
$\frac{\lambda}{4}$
$\lambda$
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
Statement I is false but Statement II is true
Statement I is true but Statement II is false
Both Statement I and Statement II are true
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:
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:
Pressure gradient
Energy
Impulse
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
9 : 4
25 : 9
2 : 1
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:
$750d$
$1098d$
$2049d$
$1500d$
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
Ba(ox) : Barium oxalate
BaCO$_3$
Ba(OAc)$_2$
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
asparagine
histidine
arginine
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:
Both Statement I and Statement II are correct
Both Statement I and Statement II are incorrect
Statement I is correct but Statement II is incorrect
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 :
Both A and R are correct but R is NOT the correct explanation of A
A is true but R is false
A is false but R is true
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
3
2
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
$\mathrm{BeO + C + F_2 \xrightarrow{\Delta}}$ $BeF_2$
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:
Both A and R are correct but R is NOT the correct explanation of A
Both A and R are correct and R is the correct explanation of A
A is not correct but R is correct
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:
Statement I is true but Statement II is false
Statement I is false but Statement II is true
Both Statement I and Statement II are false
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:
Benzoic Acid
Aniline
Salicylic Acid
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 :
A and D only
B and C only
A and B only
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
A-IV, B-II, C-III, D-I
A-IV, B-I, C-III, D-II
A-II, B-IV, C-I, D-III
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:
Both Statement I and Statement II are incorrect
Both Statement I and Statement II are correct
Statement I is incorrect but Statement II is correct
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
$\mathrm{Br}^-$ and $\mathrm{I}^-$ only
$\mathrm{Br}^-$ only
$\mathrm{I}^-$ only
$\mathrm{Cl}^-$, $\mathrm{Br}^-$ 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?
System A: Temperature rises, System B: Temperature remains same
System A: Temperature remains same, System B: Temperature rises
System A: Temperature falls, System B: Temperature remains same
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 :
A is false but R is true
Both A and R are correct and R is the correct explanation of A
A is true but R is false
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.
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
A-III, B-I, C-IV, D-II
A-I, B-II, C-III, D-IV
A-I, B-III, C-IV, D-II
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
3 and 5
3 and 4
4 and 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?
$[\mathrm{Ni(H_2O)_6}]^{2+}$
$[\mathrm{Co(en)_3}]^{3+}$
$[\mathrm{Zn(H_2O)_6}]^{2+}$
$[\mathrm{Co(H_2O)_6}]^{2+}$
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.
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)