JEE Main 15 April 2023 Shift 1 question paper with solutions

JEE Main 15 April 2023 Shift 1: 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 · Permutations and Combinations · Single correct

The total number of three-digit numbers, divisible by 3, which can be formed using the digits 1, 3, 5, 8, if repetition of digits is allowed, is

  1. 21
  2. 20
  3. 22
  4. 18

Answer: (c)

Solution

Given, three-digit number to be formed which are divisible by 3 using the digits 1, 3, 5, 8 and repetition is allowed. Now taking case (1), where all digits are same, we get $(1, 1, 1)$, $(3, 3, 3)$, $(5, 5, 5)$, $(8, 8, 8) \rightarrow 4$ ways. Now taking case (2), where 2-digit are same and one is distinct, we get $(5, 5, 8) \rightarrow \frac{3!}{2!} = 3$ ways, $(8, 8, 5) \rightarrow 3$ ways. Now taking case (3), where all are distinct, we get $(1, 3, 5) \rightarrow 6$ ways, $(1, 8, 3) \rightarrow 6$ ways. So, total ways will be $4 + 3 + 3 + 6 + 6 = 22$.

Question 2

Maths · Three Dimensional Geometry · Single correct

Let $S$ be the set of all values of $\lambda$, for which the shortest distance between the lines $\frac{x-\lambda}{0} = \frac{y-3}{4} = \frac{z+6}{1}$ and $\frac{x+\lambda}{3} = \frac{y}{-4} = \frac{z-6}{0}$ is 13. Then $8 \left| \sum_{\lambda \in S} \lambda \right|$ is equal to

  1. 306
  2. 304
  3. 308
  4. 302

Answer: (a)

Solution

The given lines are $\frac{x - \lambda}{0} = \frac{y - 3}{4} = \frac{z + 6}{1}$ and $\frac{x + \lambda}{3} = \frac{y}{-4} = \frac{z - 6}{0}$. We know that the shortest distance between two lines is $d = \frac{\left| (\vec{a_2} - \vec{a_1}) \cdot (\vec{n_1} \times \vec{n_2}) \right|}{|\vec{n_1} \times \vec{n_2}|}$ and $d = 13$ (given). $$\Rightarrow \vec{n_1} \times \vec{n_2} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 0 & 4 & 1 \\ 3 & -4 & 0 \end{vmatrix} = 4\hat{i} + 3\hat{j} - 12\hat{k}$$ Now using the above formula of distance we get, $$\Rightarrow \frac{\left| (2\lambda \hat{i} + 3\hat{j} - 12\hat{k}) \cdot (4\hat{i} + 3\hat{j} - 12\hat{k}) \right|}{\sqrt{16 + 9 + 144}} = 13$$ $$\Rightarrow \frac{\left| (2\lambda \hat{i} + 3\hat{j} - 12\hat{k}) \cdot (4\hat{i} + 3\hat{j} - 12\hat{k}) \right|}{13} = 13$$ $$\Rightarrow |8\lambda + 9 + 144| = 169$$ $$\Rightarrow |8\lambda + 153| = 169$$ $$\Rightarrow 8\lambda = \pm 169 - 153$$ $$\Rightarrow \lambda = \frac{16}{8}, \frac{-322}{8}$$ $$\Rightarrow 8\left| \sum_{\lambda \in S} \lambda \right| = 8 \left| \frac{16}{8} - \frac{322}{8} \right|=306$$ Hence this is the correct option.

Question 3

Maths · Statistics · Single correct

The mean and standard deviation of 10 observations are 20 and 8 respectively. Later on, it was observed that one observation was recorded as 50 instead of 40. Then the correct variance is

  1. 11
  2. 13
  3. 12
  4. 14

Answer: (b)

Solution

Incorrect mean is $$\frac{\sum_{i=1}^{10} x_i}{10} = 20$$ which implies $$\sum_{i=1}^{10} x_i = 200 \cdots (i)$$ So, corrected mean is $$\frac{\sum_{i=1}^{10} x_i - 50 + 40}{10} = \frac{200 - 10}{10} = 19$$ Incorrect variance is $$\frac{\sum_{i=1}^{10} x_i^2}{10} - 400 = 64$$ which implies $$\sum_{i=1}^{10} x_i^2 = 4640$$ Now, corrected variance is $$= \frac{\sum_{i=1}^{9} x_i^2 + 40^2 - 50^2}{10} - (19)^2$$ $$= \frac{4640 - 900}{10} - (19)^2$$ $$= 374 - 361$$ $$= 13$$

Question 4

Maths · Vector Algebra · Single correct

Let ABCD be a quadrilateral. If E and F are the mid points of the diagonals AC and BD respectively and ( $\overrightarrow{AB}$ - $\overrightarrow{BC}$ ) + ( $\overrightarrow{AD}$ - $\overrightarrow{DC}$ ) = k $\overrightarrow{FE}$, then k is equal to

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

Answer: (d)

Solution

Given, $\($ABCD$\)$ be a quadrilateral. If $\($E$\)$ and $\($F$\)$ are the midpoints of the diagonals $\($AC$\)$ and $\($BD$\)$ respectively and $\($$\left$( $\overrightarrow{AB}$ - $\overrightarrow{BC}$ $\right$) + $\left$( $\overrightarrow{AD}$ - $\overrightarrow{DC}$ $\right$) = k $\overrightarrow{FE}$$\)$, Now plotting the diagram we get, Now let position vector of $\($A, B, C$\)$ and $\($D$\)$ are $\($$\overrightarrow{a}$, $\overrightarrow{b}$, $\overrightarrow{c}$$\)$ and $\($$\overrightarrow{d}$$\)$ respectively. Now by midpoint formula, Position vector of $\($E = $\frac{\overrightarrow{OC} + \overrightarrow{OA}}{2}$ = $\frac{\overrightarrow{c} + \overrightarrow{a}}{2}$$\)$ And Position vector of $\($F = $\frac{\overrightarrow{b} + \overrightarrow{d}}{2}$$\)$ Now, $\($$\left$( $\overrightarrow{AB}$ - $\overrightarrow{BC}$ $\right$) + $\overrightarrow{AD}$ - $\overrightarrow{DC}$$\)$ $\($$\Rightarrow$ $\overrightarrow{b}$ - $\overrightarrow{a}$ - $\left$( $\overrightarrow{c}$ - $\overrightarrow{b}$ $\right$) + $\overrightarrow{d}$ - $\overrightarrow{a}$ - $\left$( $\overrightarrow{c}$ - $\overrightarrow{d}$ $\right$)$\)$ $\($$\Rightarrow$ 2 $\overrightarrow{b}$ - 2 $\overrightarrow{a}$ - 2 $\overrightarrow{c}$ + 2 $\overrightarrow{d}$$\)$ $\($$\Rightarrow$ 2 $\left$( $\overrightarrow{b}$ + $\overrightarrow{d}$ $\right$) - 2 $\left$( $\overrightarrow{a}$ + $\overrightarrow{c}$ $\right$)$\)$ $\($$\Rightarrow$ 4 $\left$[ $\frac{\overrightarrow{b} + \overrightarrow{d}}{2}$ - $\frac{\overrightarrow{a} + \overrightarrow{c}}{2}$ $\right$] = 4 $\left$[ $\overrightarrow{OF}$ - $\overrightarrow{OE}$ $\right$]$\)$ $\($$\Rightarrow$ 4 $\overrightarrow{EF}$ = -4 $\overrightarrow{FE}$$\)$ $\($$\therefore$ k = -4$\)$

Question 5

Maths · Differential Equations · Single correct

Let $x = x(y)$ be the solution of the differential equation $2(y+2)\log_e(y+2)dx +(x+4-2\log_e(y+2))dy=0$, $y>-1$ with $x(e^4-2)=1$. Then $x(e^9-2)$ is equal to

  1. 3
  2. $\frac{4}{9}$
  3. $\frac{32}{9}$
  4. $\frac{10}{3}$

Answer: (c)

Solution

Given, $$2(y+2)\log_e(y+2)dx+(x+4-2\log_e(y+2))dy=0$$ Let $x+4=u$, $y+2=v$ $$dx=du, \; dy=dv$$ So, the equation becomes, $$(2v \ln v)du = -(u-2 \ln v)dv$$ $$\Rightarrow 2v \ln v \frac{du}{dv} + u = 2 \ln v$$ $$\Rightarrow \frac{du}{dv} + \frac{1}{2v \ln v} \cdot u = \frac{1}{v}$$ Which is a linear differential equation, So, $IF = e^{\int \frac{1}{v \ln v} = e^{\frac{1}{2} \ln (\ln v)} = (\ln v)^{\frac{1}{2}}}$ Now solution of differential equation is given by, $$u \cdot (\ln v)^{\frac{1}{2}} = \int \frac{1}{v} \cdot (\ln v)^{\frac{1}{2}} dv$$ $$\Rightarrow u \cdot (\ln v)^{\frac{1}{2}} = \frac{2}{3} (\ln v)^{\frac{3}{2}} + c \ldots \ldots \ldots (i)$$ Now using given value, $y = e^4 - 2 \Rightarrow x = 1$ $$\therefore \; v = e^4 \Rightarrow u = 5$$ $$5 \cdot \left(\frac{1}{4}\right)^{\frac{1}{2}} = \frac{2}{3} \cdot (4)^{\frac{3}{2}} + c$$ $$\Rightarrow 10 = \frac{16}{3} + c$$ $$\Rightarrow c = \frac{14}{3}$$ Now finding, $y = e^9 - 2 \Rightarrow v = y + 2 = e^9$ Now putting the value in equation (i) we get, $$\Rightarrow u \cdot 3 = 2 \times 27 + \frac{14}{3} = 18 + \frac{14}{3}$$ $$\Rightarrow x + 4 = u = 6 + \frac{14}{9}$$ $$\Rightarrow x = 2 + \frac{14}{9} = \frac{32}{9}$$

Question 6

Maths · Continuity and Differentiability · Single correct

Let [x] denote the greatest integer function and $f(x) = \max\{1 + x + [x], 2 + x, x + 2[x]\}$, $0 \leq x \leq 2$, where $f$ is not continuous and $n$ be the number of points in $(0, 2)$, where $f$ is not differentiable. Then $(m + n)^2 + 2$ is equal to

  1. 2
  2. 11
  3. 6
  4. 3

Answer: (d)

Solution

Given, $$f(x) = \max \{ 1 + x + \lfloor x \rfloor,\; 2 + x,\; x + 2 \lfloor x \rfloor \},\; 0 \leq x \leq 2$$ $$\Rightarrow f(x) =$$ $\max \{ x + 1,\; x + 2,\; x \}$ , $0 \leq x < 1$ $\max \{ x + 2,\; x + 2,\; x + 2 \}$ , $1 \leq x < 2$ $\max \{ 5,\; 4,\; 6 \}$ , $x = 2$ $$\Rightarrow f(x) =$$ $x + 2$, $0 \leq x < 1$ $x + 2$, $1 \leq x < 2$ $6$, $x = 2$ $$\Rightarrow f(x) =$$ $x + 2$, $0 \leq x < 2$ $6$, $x = 2$ So, $f$ is not continuous at $x = 2$ as $f(2^-) = 4$ and $f(2) = 6$. And $f$ is differentiable in $(0, 2)$ as $x + 2$ is a linear function, $$\therefore\ m = 1,\; n = 0$$ $$\Rightarrow (m + n)^2 + 2 = 1 + 2 = 3$$ Hence this is the required option.

Question 7

Maths · Complex Numbers and Quadratic Equations · Single correct

The number of real roots of the equation $x|x-5|x+2|+6=0$, is

  1. 5
  2. 4
  3. 6
  4. 3

Answer: (d)

Solution

Given, $$x|x|-5|x+2|+6=0$$ Now taking case (1) when $x < -2$ we get, $$-x^2 + 5x + 10 + 6 = 0$$ $$\Rightarrow x^2 - 5x - 16 = 0$$ $$\Rightarrow x = \frac{5-\sqrt{89}}{2}, ignoring x = \frac{5+\sqrt{89}}{2} as x < -2, so one solution is possible here,$$ Now taking case (2) when $-2 \leq x < 0$ we get, $$-x^2 - 5x - 10 + 6 = 0$$ $$\Rightarrow x^2 + 5x + 4 = 0$$ $$\Rightarrow x = -1, ignoring x = -4 as -2 \leq x < 0$$ Now taking case (3), when $x \geq 0$ we get, $$x^2 - 5x - 10 + 6 = 0$$ $$\Rightarrow x^2 - 5x - 4 = 0$$ $$\Rightarrow x = \frac{5+\sqrt{41}}{2}, ignoring x = \frac{5-\sqrt{41}}{2} as x \geq 0$$ So, from all cases we get total 3 solutions.

Question 8

Maths · Binomial Theorem · Single correct

Let $(a+bx+cx^2)^{10} = \sum_{i=10}^{20} p_i x^i$, $a$, $b$, $c \in \mathbb{N}$. If $p_1 = 20$ and $p_2 = 210$, then $2(a+b+c)$ is equal to

  1. 6
  2. 15
  3. 12
  4. 8

Answer: (c)

Solution

Given that $(a + bx + cx^2)^{10} = \sum_{i=10}^{20} p_i x^i$, $a, b, c \in \mathbb{N}$. General term: $$\frac{10!}{r_1! \, r_2! \, r_3!} (a)^{r_1} (bx)^{r_2} (cx^2)^{r_3}$$ For coefficient of $x$: $r_2 + 2r_3 = 1$. Let $$\begin{array}{ccc} r_1 & r_2 & r_3 \\ 9 & 1 & 0 \end{array}$$ Therefore, coefficient of $x = \frac{10!}{9!} a^9 b^1 = 20$. $$\Rightarrow a^9 \cdot b = 2 \ldots \ldots (i)$$ Coefficient of $x^2$: $$\frac{10!}{8! \, 2! \, 0!} a^8 \cdot b^2 + \frac{10!}{9! \, 0! \, 1!} a^9 \cdot c = 210$$ $$\Rightarrow 45a^8 \cdot b^2 + 10 \cdot a^9 \cdot c = 210$$ $$\Rightarrow 9a^8 b^2 + 2a^9 \cdot c = 42 \ldots \ldots (ii)$$ As $a, b, c \in \mathbb{N}$, so by hit and trial in equation (i) $\&$ (ii) we get, $a = 1, b = 2, c = 3$. Hence, $2(a + b + c) = 2(3 + 2 + 1) = 12$.

Question 9

Maths · Matrices · Single correct

Let the determinant of a square matrix $A$ of order $m = n$, where $m$ and $n$ satisfy $4m + n = 22$ and $17m + 4n = 93$. If $\det(n \; \mathrm{adj}(\mathrm{adj}(mA))) = 3^a 5^b 6^c$, then $a + b + c$ is equal to

  1. 84
  2. 96
  3. 101
  4. 109

Answer: (b)

Solution

We have been given that $|A| = m - n$, where $4m + n = 22 \ldots (i)$ and $17m + 4n = 93 \ldots (ii)$. Solving (i) and (ii) $m = 5$, $n = 2$. Order $= 5$. Therefore, $|A| = 3$. We know that $|adj A| = |A|^{w-1} |adj (adj A)| = |A|^{(w-1)^2}$ where $w \times w$ is the order of the matrix. Therefore, $\det (n adj (adj (mA))) = |2 adj (adj (5A))| = 2^5 |5A|^{16} = 2^5 5^{80} |A|^{16} = 2^5 \cdot 3^{16} \cdot 5^{80} = 3^{11} 5^{80} 6^5$. So, $a + b + c = 96$. Hence this is the required option.

Question 10

Maths · Sequences and Series · Single correct

Let $A_1$ and $A_2$ be two arithmetic means and $G_1$, $G_2$ and $G_3$ be three geometric means of two distinct positive numbers. Then $G_1^4 + G_2^4 + G_3^4 + G_1^2 G_3^2$ is equal to

  1. $(A_1 + A_2)^2 G_1 G_3$
  2. $2(A_1 + A_2) G_1 G_3$
  3. $(A_1 + A_2) G_1^2 G_3^2$
  4. $2(A_1 + A_2) G_1^2 G_3^2$

Answer: (a)

Solution

Let the two numbers are $a$, $b$. $a$, $A_1$, $A_2$, $b$ are in AP. $b = a + (4 - 1)d$ $d = \frac{b-a}{3}$ $A_1 = a + \frac{b-a}{3} = \frac{2a+b}{3}$ $A_2 = a + \frac{b-a}{3} \cdot 2 = \frac{a+2b}{3}$ Similarly $a$, $G_1$, $G_2$, $G_3$, $b$ are in GP. $b = a(r)^{5-1}$ $r = \left(\frac{b}{a}\right)^{\frac{1}{4}}$ $G_1 = a\left(\frac{b}{a}\right)^{\frac{1}{4}}$ $G_2 = a\left(\frac{b}{a}\right)^{\frac{2}{4}}$ $G_3 = a\left(\frac{b}{a}\right)^{\frac{3}{4}}$ $(G_1)^4 + (G_2)^4 + (G_3)^4 + (G_1)^2 \cdot (G_3)^2$ $= a^4 \cdot \frac{b}{a} + a^4 \cdot \frac{b^2}{a^2} + a^4 \cdot \frac{b^3}{a^3} + a^4 \cdot \frac{b^2}{a^2}$ $= ba^3 + b^2a^2 + b^3a + a^2b^2$ $= ab(a^2 + b^2 + 2ab) = ab(a+b)^2$ $(A_1 + A_2)^2 \cdot G_1 G_3 = (a+b)^2 \cdot ab$ Hence this is the correct option.

Question 11

Maths · Complex Numbers and Quadratic Equations · Single correct

If the set $\left\{ \mathrm{Re} \left( \frac{z - \bar{z} + z \bar{z}}{2 - 3z + 5\bar{z}} \right) : z \in \mathbb{C},\; \mathrm{Re}\,(z) = 3 \right\}$ is equal to the interval $(\alpha,\beta]$, then $24(\beta - \alpha)$ is equal to

  1. 36
  2. 27
  3. 30
  4. 42

Answer: (c)

Solution

Given that the set $\left\{ \Re \left( \frac{z - \bar{z} + z^2}{2 - 3z + 5\bar{z}} \right) : z \in \mathbb{C}, \ \Re z = 3 \right\}$ is equal to the interval $(\alpha, \beta)$. Let $z = x + iy$. $$= \Re \left( \frac{x + iy - (x - iy) + x^2 + y^2}{2 - 3(x + iy) + 5(x - iy)} \right)$$ $$= \Re \left( \frac{x^2 + y^2 + i(2y)}{2 + 2x - 8iy} \right)$$ $$= \Re \left( \frac{(x^2 + y^2 + 2yi)(2(1 + x) + 8iy)}{(2(1 + x))^2 + (8y)^2} \right)$$ $$= \frac{2(x^2 + y^2)(1 + x) - 16y^2}{4(1 + x)^2 + (8y)^2}$$ Now using, $\Re(z) = 3 \Rightarrow x = 3$ we get, $$\frac{8(9 + y^2) - 16y^2}{64 + 64y^2}$$ $$\Rightarrow f(y) = \frac{1}{8} \left( \frac{9 - y^2}{1 + y^2} \right)$$ Let $t = \frac{1}{8} \cdot \frac{1}{1 + y^2}$ $$\Rightarrow 8t + 8ty^2 = 9 - y^2$$ $$\Rightarrow y^2(8t + 1) + 8t - 9 = 0$$ Now $D \geq 0$ $$\Rightarrow 0^2 - 4(8t + 1)(8t - 9) \geq 0$$ $$\Rightarrow \left( t - \left( -\frac{1}{8} \right) \right) \left( t - \frac{9}{8} \right) \leq 0$$ $$\Rightarrow t \in \left( -\frac{1}{8}, \frac{9}{8} \right) as t \neq -\frac{1}{8}$$ Range of $f(y) = (-0.125, 1.125)$ $$\Rightarrow \alpha = -0.125$$ $$\Rightarrow \beta = 1.125$$ $$\Rightarrow \beta - \alpha = 1.25$$ $$\Rightarrow 24(\beta - \alpha) = 30$$ Hence this is the required solution.

Question 12

Maths · Conic Sections · Single correct

The number of common tangents, to the circles $x^2 + y^2 - 18x - 15y + 131 = 0$ and $x^2 + y^2 - 6x - 6y - 7 = 0$, is

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

Answer: (a)

Solution

If $S = x^2 + y^2 + 2gx + 2fy + c = 0$ $C = (-g,\,-f)$ and $r = \sqrt{g^2 + f^2 - c}$ The given circles are $x^2 + y^2 - 18x - 15y + 131 = 0$ $\Rightarrow C_1(9,\; \frac{15}{2}),\quad r_1 = \sqrt{81 + \frac{225}{4} - 131} = \frac{3}{2}$ and $x^2 + y^2 - 6x - 6y - 7 = 0$ $\Rightarrow C_2(3,\; 3),\quad r_2 = \sqrt{9 + 9 + 7} = 5$ $$d = C_1C_2 = \sqrt{(9-3)^2 + \left(\frac{15}{2}-3\right)^2} = \sqrt{36 + \frac{81}{4}} = \frac{15}{2}$$ $$r_1 + r_2 = \frac{3}{2} + 5 = \frac{13}{2}$$ $$\therefore C_1C_2 = r_1 + r_2$$ $\therefore$ Circles touch externally, 3 common tangents. Hence this is the correct option.

Question 13

Maths · Mathematical Reasoning · Single correct

Negation of $p \land (q \land \sim (p \land q))$ is

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

Answer: (a)

Solution

Given, Expression $p \land (q \land \sim (p \land q))$ So, negation of the above expression will be, $$\sim [p \land (q \land \sim (p \land q))]$$ Now using demorgan's law $\sim (A \land B) \equiv \sim A \lor \sim B$ we get, $$\sim [p \land (q \land \sim (p \land q))]$$ $$\equiv \sim [p \land (q \land (\sim p \lor \sim q))]$$ $$\equiv \sim [p \land ((q \land \sim p) \lor (q \land \sim q))]$$ $$\equiv \sim [p \land ((q \land \sim p) \lor F)]$$ $$\equiv \sim [p \land (q \land \sim p)]$$ $$\equiv \sim p \lor \sim (q \land \sim p)$$ $$\equiv \sim p \lor (\sim q \lor p)$$ $$\equiv (\sim p \lor \sim q) \lor p$$ $$\equiv p \lor \sim q \lor p$$

Question 14

Maths · Determinants · Single correct

Let the system of linear equations $$-x + 2y - 9z = 7$$ $$-x + 3y + 7z = 9$$ $$-2x + y + 5z = 8$$ $$-3x + y + 13z = \lambda$$ has a unique solution $x = \alpha$, $y = \beta$, $z = \gamma$. Then the distance of the point $(\alpha, \beta, \gamma)$ from the plane $2x - 2y + z = \lambda$ is

  1. 11
  2. 7
  3. 9
  4. 13

Answer: (b)

Solution

Given, System of linear equation, $$-x + 2y - 9z = 7 \ldots \ldots (i)$$ $$-x + 3y + 7z = 9 \ldots \ldots (ii)$$ $$-2x + y + 5z = 8 \ldots \ldots (iii)$$ $$-3x + y + 13z = \lambda \ldots \ldots (iv)$$ Now solving, equations (i), (ii) & (iii) we get, $$x = -3, \ y = 2, \ z = 0$$ Now substituting in equation (iv) we get, $$3 \times 3 + 2 = \lambda$$ $$\Rightarrow \lambda = 11$$ Now finding the distance of Point $(-3, 2, 0)$ from the plane $2x - 2y + z = 11$ we get, $$d = \left| \frac{-6 - 4 - 11}{\sqrt{2^2 + 2^2 + 1}} \right| = \left| \frac{21}{3} \right| = 7$$

Question 15

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

If $(\alpha, \beta)$ is the orthocenter of the triangle $ABC$ with vertices $A(3, -7)$, $B(-1, 2)$ and $C(4, 5)$, then $9\alpha - 6\beta + 60$ is equal to

  1. 25
  2. 35
  3. 30
  4. 40

Answer: (a)

Solution

The required diagram will be: Equation of $AD$: $y + 7 = \frac{-5}{3}(x - 3)$ $$\Rightarrow 3y + 21 = -5x + 15$$ $$\Rightarrow 5x + 3y + 6 = 0 \ldots \ldots (i)$$ Equation of $BE$: $y - 2 = \frac{-1}{12}(x + 1)$ $$\Rightarrow 12y - 24 = -x - 1$$ $$\Rightarrow x = 23 - 12y \ldots (ii)$$ By (ii) $115 - 60y + 3y + 6 = 0$ $$\Rightarrow 57y = 121$$ $$y = \frac{121}{57}, x = 23 - 12 \times \frac{121}{57}$$ Therefore, $9\alpha - 6\beta + 60 = 9 \times 23 - 108 \times \frac{121}{57} - 6 \times \frac{121}{57} + 60$ $$= 207 - 242 + 60 = 25$$ Hence this is the required option.

Question 16

Maths · Three Dimensional Geometry · Single correct

Let the foot of perpendicular of the point $P(3, -2, -9)$ on the plane passing through the points $(-1, -2, -3)$, $(9, 3, 4)$, $(9, -2, 1)$ be $Q(\alpha, \beta, \gamma)$. Then the distance $Q$ from the origin is

  1. $\sqrt{42}$
  2. $\sqrt{38}$
  3. $\sqrt{35}$
  4. $\sqrt{29}$

Answer: (a)

Solution

Given that three points lie on a plane, $$\overrightarrow{AC} = 10\hat{i} + 4\hat{k}$$ $$\overrightarrow{AB} = 10\hat{i} + 5\hat{j} + 7\hat{k}$$ $$\overrightarrow{AC} \times \overrightarrow{AB} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 10 & 0 & 4 \\ 10 & 5 & 7 \end{vmatrix}$$ $$\overrightarrow{AC} \times \overrightarrow{AB} = -20\hat{i} - 30\hat{j} + 50\hat{k}$$ $$\Rightarrow \overrightarrow{AC} \times \overrightarrow{AB} = 2\hat{i} + 3\hat{j} - 5\hat{k}$$ Equation of plane will be, $$\Rightarrow 2x + 3y - 5z = d$$ And the plane passing through, $(-1, -2, -3)$ $$\Rightarrow -2 - 6 + 15 = d$$ $$\Rightarrow d = 7$$ $$\therefore 2x + 3y - 5z = 7$$ Now finding the foot of perpendicular we get, $$\frac{x-3}{2} = \frac{y+2}{3} = \frac{z+9}{-5} = -\left(\frac{38}{38}\right)$$ $$x = 1, \ y = -5, \ z = -4$$ $Q(1, -5, -4)$ Distance from origin = $\sqrt{1^2 + 25 + 16} = \sqrt{42}$ Hence this is the required option.

Question 17

Maths · Probability · Single correct

A bag contains 6 white and 4 black balls. A die is rolled once and the number of balls equal to the number obtained on the die are drawn from the bag at random. The probability that all the balls drawn are white is

  1. $\frac{1}{4}$
  2. $\frac{11}{50}$
  3. $\frac{1}{5}$
  4. $\frac{9}{50}$

Answer: (c)

Solution

Given, Bag have 6 white and 4 black balls. Now also given die is rolled and the number denotes the number of ball drawn from the bag. So, probability all drawn balls are white will be, $$= \frac{1}{6} \left[ \frac{{^6C_1}}{{^{10}C_1}} + \frac{{^6C_2}}{{^{10}C_2}} + \frac{{^6C_3}}{{^{10}C_3}} + \frac{{^6C_4}}{{^{10}C_4}} + \frac{{^6C_5}}{{^{10}C_5}} + \frac{{^6C_6}}{{^{10}C_6}} \right]$$ $$= \frac{1}{6} \left[ \frac{6}{10} + \frac{15}{45} + \frac{20}{120} + \frac{15}{210} + \frac{6}{252} + \frac{1}{210} \right]$$ $$= \frac{504}{2520} = \frac{1}{5}$$

Question 18

Maths · Integrals · Single correct

If $\int_0^1 \frac{1}{(5+2x-2x^2)} \frac{1}{(1+e^{(2-4x)})} \, dx = \frac{1}{\alpha} \log_e \left( \frac{\alpha+1}{\beta} \right)$, $\alpha, \beta > 0$, then $\alpha^4 - \beta^4$ is equal to

  1. 19
  2. -21
  3. 0
  4. 21

Answer: (d)

Solution

Given, $$\int_0^1 \frac{1}{(5+2x-2x^2)(1+e^{1-4x})} \, dx = \frac{\alpha}{\beta} \log_e \left( \frac{\alpha+1}{\beta} \right)$$ Now let, $$I = \frac{1}{2} \int_0^1 \frac{1}{\left( 5 - (x^2 - x) \right) \left( 1 + e^{1-4x} \right)} \, dx$$ $$\Rightarrow I = \frac{1}{2} \int_0^1 \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - \left( x - \frac{1}{2} \right)^2} \frac{1}{\left( 1 + e^{1-4x} \right)} \, dx$$ Now let $x = \frac{1}{2} + t \Rightarrow dx = dt$ So, integral becomes, $$I = \frac{1}{2} \int_{-\frac{1}{2}}^{\frac{1}{2}} \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{\left( 1 + e^{1-4t} \right)} \, dt$$ $$\Rightarrow I = \frac{1}{2} \int_0^{\frac{1}{2}} \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{\left( 1 + e^{1-4t} \right)} \, dt + \frac{1}{2} \int_0^{\frac{1}{2}} \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{\left( 1 + e^{4t-1} \right)} \, dt$$ Now solving $I_2 = \frac{1}{2} \int_0^{\frac{1}{2}} \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{\left( 1 + e^{4t-1} \right)} \, dt,$ Let $t = -z$, we get $dt = -dz$ So, $$I_2 = -\frac{1}{2} \int_{\frac{1}{2}}^0 \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - (-z)^2} \frac{1}{\left( 1 + e^{4(-z)-1} \right)} \, dz$$ $$\Rightarrow I_2 = \frac{1}{2} \int_0^{\frac{1}{2}} \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{\left( 1 + e^{1-4t} \right)} \, dt$$ Now putting the value of $I_2$ in $I$ we get, $$I = \frac{1}{2} \int_0^{\frac{1}{2}} \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{\left( 1 + e^{1-4t} \right)} \, dt + \left( \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \right) \frac{1}{\left( 1 + e^{1-4t} \right)} \, dt$$ $$\Rightarrow I = \int_0^{\frac{1}{2}} \frac{e^{4t}}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{(e^{4t}+1)} \, dt + \left( \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \right) \frac{1}{\left( 1 + e^{1-4t} \right)} \, dt$$ $$\Rightarrow I = \frac{1}{2} \int_0^{\frac{1}{2}} \frac{1}{\left( \frac{\sqrt{11}}{2} \right)^2 - t^2} \frac{1}{\left( 1 + e^{1-4t} \right)} \, dt$$ $$\Rightarrow I = \frac{1}{2} \times \frac{1}{\sqrt{11}} \left[ \ln \left| \frac{\sqrt{11}+1}{\sqrt{11}-1} \right| \right]_0^{\frac{1}{2}}$$ $$\Rightarrow I = \frac{1}{\sqrt{11}} \ln \left( \frac{\sqrt{11}+1}{\sqrt{11}-1} \right) = \frac{1}{\sqrt{11}} \ln \left( \frac{(\sqrt{11})^2}{10} \right)$$ $$\Rightarrow I = \frac{1}{\sqrt{11}} \ln \left( \frac{\sqrt{11}+1}{\sqrt{11}-1} \right)$$ Now on comparing with $\frac{\alpha}{\beta} \log_e \left( \frac{\alpha+1}{\beta} \right)$ we get, $$\Rightarrow \alpha = \sqrt{11}, \beta = \sqrt{10} \Rightarrow \alpha^4 - \beta^4 = 21$$

Question 19

Maths · Vector Algebra · Single correct

Let S be the set of all $(\lambda, \mu)$ for which the vectors $\lambda \hat{i} - \hat{j} + \hat{k}$, $\hat{j} + 2 \hat{j} + \mu \hat{k}$ and $3 \hat{i} - 4 \hat{j} + 5 \hat{k}$, where $\lambda - \mu = 5$, are coplanar, then $\sum_{(\lambda, \mu) \in S} 80 (\lambda^2 + \mu^2)$ is equal to

  1. 2210
  2. 2130
  3. 2290
  4. 2370

Answer: (c)

Solution

The given equations are coplanar. $$\begin{vmatrix} \lambda & -1 & 1 \\ 1 & 2 & \mu \\ 3 & -4 & 5 \end{vmatrix} = 0$$ $$\Rightarrow \lambda [10 + 4\mu] + 1[5 - 3\mu] + 1[-10] = 0$$ $$\Rightarrow 4\lambda \mu + 10\lambda - 3\mu = 5 \ldots \ldots (i)$$ And $\lambda - \mu = 5$ So, by (1) $$\Rightarrow 4(5 + \mu)\mu + 10(5 + \mu) - 3\mu = 5$$ $$\Rightarrow 4\mu^2 + 27\mu + 45 = 0$$ $$\Rightarrow 4\mu^2 + 15\mu + 12\mu + 45 = 0$$ $$\therefore \mu = -3, \frac{-15}{4}$$ $$\Rightarrow \lambda = 2, \frac{5}{4}$$ $$\therefore \sum_{\lambda, \mu \in S} 80(\lambda^2 + \mu^2) = 80 \left[ (9 + 4) + \frac{225}{16} + \frac{25}{16} \right]$$ $$= 80 \left[ 13 + \frac{125}{8} \right] = 10 \times 229$$ $$= 2290$$ Hence this is the correct option.

Question 20

Maths · Relations and Functions · Single correct

If the domain of the function $f(x) = \log_e (4x^2 + 11x + 6) + \sin^{-1}(4x + 3) + \cos^{-1}\left(\frac{10x + 6}{3}\right)$ is $(\alpha, \beta]$, then $36|\alpha + \beta|$ is equal to

  1. 54
  2. 72
  3. 63
  4. 45

Answer: (d)

Solution

Given that $f(x) = \log(4x^2 + 11x + 6) + \sin^{-1}(4x + 3) + \cos^{-1}\left(\frac{10x + 6}{3}\right)$. We know that the domain of $A(x) + B(x) + C(x)$ is $D(A) \cap D(B) \cap D(C)$. Let us find the domain of $\log(4x^2 + 11x + 6)$. We know that domain of $\log(f(x))$ is $f(x) > 0$. $$4x^2 + 11x + 6 > 0$$ $$4x^2 + 8x + 3x + 6 > 0$$ $$(4x + 3)(x + 2) > 0$$ $$x \in (-\infty, -2) \cup \left(-\frac{3}{4}, \infty\right).$$ Domain of $\log(4x^2 + 11x + 9)$ is $x \in (-\infty, -2) \cup \left(-\frac{3}{4}, \infty\right)$. Let us find the domain of $\sin^{-1}(4x + 3)$ $$-1 \leq 4x + 3 \leq 1$$ $$-1 \leq x \leq -\frac{1}{2}$$ $$x \in \left[-1, -\frac{1}{2}\right]$$ Let us find the domain of $\cos^{-1}\left(\frac{10x+6}{3}\right)$. $$-1 \leq \frac{10x+6}{3} \leq 1$$ $$-3 \leq 10x + 6 \leq 3$$ $$-\frac{9}{10} \leq x \leq -\frac{3}{10}$$ Now the common domain is $$-\frac{3}{4} \leq x \leq -\frac{1}{2}.$$ $$x \in \left[-\frac{3}{4}, -\frac{1}{2}\right].$$ But given that the domain of $f(x)$ is $x \in [\alpha, \beta]$. $$\alpha = -\frac{3}{4}, \ \beta = -\frac{1}{2}.$$ $$\Rightarrow |36(\alpha + \beta)| = \left|36\left(-\frac{3}{4} + \left(-\frac{1}{2}\right)\right)\right|$$ $$\Rightarrow |36(\alpha + \beta)| = \left|36 \times \frac{-5}{4}\right|$$ $$\Rightarrow |36(\alpha + \beta)| = 45$$ Therefore, the required answer is 45.

Question 21

Maths · Sequences and Series · Numerical

If the sum of the series $$\left( \frac{1}{2} - \frac{1}{3} \right) + \left( \frac{1}{2^2} - \frac{1}{2 \cdot 3} + \frac{1}{3^2} \right) + \left( \frac{1}{2^3} - \frac{1}{2^2 \cdot 3} + \frac{1}{2 \cdot 3^2} - \frac{1}{3^3} \right) + \left( \frac{1}{2^4} - \frac{1}{2^3 \cdot 3} + \frac{1}{2^2 \cdot 3^2} - \frac{1}{2 \cdot 3^3} + \frac{1}{3^4} \right) + \ldots$$ is $\frac{\alpha}{\beta}$, where $\alpha$ and $\beta$ are co-prime, then $\alpha + 3\beta$ is equal to _______.

Answer: 7

Solution

Given, Series $\left( \frac{1}{2} - \frac{1}{3} \right) + \left( \frac{1}{2^2} - \frac{1}{2 \cdot 3} + \frac{1}{3^2} \right) + \left( \frac{1}{2^3} - \frac{1}{2^2 \cdot 3} + \frac{1}{2 \cdot 3^2} - \frac{1}{3^3} \right) + \left( \frac{1}{2^4} - \frac{1}{2^3 \cdot 3} + \frac{1}{2^2 \cdot 3^2} - \frac{1}{2 \cdot 3^3} + \frac{1}{3^4} \right) + \ldots$ Now let $a = \frac{1}{2}$, $b = \frac{1}{3}$ So, series will be: $(a - b) + (a^2 - ab + b^2) + (a^3 - a^2 b + ab^2 - b^3) + \ldots$ $$= \frac{1}{a+b} \left( (a^2 - b^2) + (a^3 + b^3) + (a^4 - b^4) + \ldots \right)$$ $$= \left( \frac{1}{a+b} \right) \left( a^2 + a^3 + a^4 \ldots - (b^2 - b^3 + b^4 \ldots) \right)$$ Now using infinite G.P. formula we get, $$= \left( \frac{1}{a+b} \right) \left( a^2 + a^3 + a^4 \ldots - (b^2 - b^3 + b^4 \ldots) \right)$$ $$= \left( \frac{1}{a+b} \right) \left( \frac{a^2}{1-a} - \frac{b^2}{1+b} \right)$$ Now putting the value of $a$ and $b$ we get, $$= \frac{1}{\frac{1}{2} + \frac{1}{3}} \left( \frac{1}{4} - \frac{1}{9} \right) \left( \frac{1}{1 - \frac{1}{2}} - \frac{1}{1 + \frac{1}{3}} \right)$$ $$= \frac{6}{5} \left( \frac{1}{2} - \frac{1}{12} \right)$$ $$= \frac{6}{5} \left( \frac{5}{12} \right) = \frac{1}{2} = \frac{\alpha}{\beta}$$ Hence, $\alpha + 3 \beta = 1 + 6 = 7$

Question 22

Maths · Permutations and Combinations · Numerical

A person forgets his 4-digit ATM pin code. But he remembers that in the code all the digits are different, the greatest digit is 7 and the sum of the first two digits is equal to the sum of the last two digits. Then the maximum number of trials necessary to obtain the correct code is _______.

Answer: 72

Solution

\[ \lambda=7,\quad (a,b)\to(0,7)\ \text{or}\ (7,0), \] then \[ (c,d)\to(1,6),(2,5),(3,4),(4,3),(5,2),(6,1) \] and vice-versa, so \[ 2\times 12=24 \] numbers. \[ \lambda=8,\quad (a,b)\to(1,7)\ \text{or}\ (7,1), \] then \[ (c,d)\to(2,6),(3,5),(6,2),(5,3) \] and vice-versa, so total \[ 2\times 8=16 \] numbers. \[ \lambda=9,\quad (a,b)\to(2,7)\ \text{or}\ (7,2), \] then \[ (c,d)\to(3,6),(4,5),(5,4),(6,3) \] and vice-versa, so total \[ 2\times 8=16 \] numbers. \[ \lambda=10,\quad (a,b)\to(3,7),(7,3), \] so \[ (c,d)\to(6,4),(4,6) \] \[ \Rightarrow 8\ \text{numbers} \] \[ \lambda=11,\quad (a,b)\to(4,7),(7,4), \] so \[ (c,d)\to(6,5),(5,6) \] \[ \Rightarrow 8\ \text{numbers} \] \[ \lambda=12,13\ \&\ 14 \] are not possible. $\therefore$ Total numbers = 24+16+16+8+8 = 72.

Question 23

Maths · Three Dimensional Geometry · Numerical

Let the plane $P$ contain the line $2x + y - z - 3 = 0 = 5x - 3y + 4z + 9$ and be parallel to the line $\frac{x+2}{2} = \frac{3-y}{-4} = \frac{z-7}{5}$. Then the distance of the point $A(8, -1, -19)$ from the plane $P$ measured parallel to the line $\frac{x}{-3} = \frac{y-5}{4} = \frac{2-z}{-12}$ is equal to .

Answer: 26

Solution

Let the Plane containing the line $2x + y - 3 - 3 = 0 = 5x - 3y + 4z + 9$ is given by, $$2x + y - z - 3 + \lambda(5x - 3y + 4z + 9) = 0$$ $$\Rightarrow x(2 + 5\lambda) + y(1 - 3\lambda) + z(4\lambda - 1) + 9\lambda - 3 = 0$$ Also, this plane is parallel to the line $$\frac{x+2}{2} = \frac{3y-4}{-3} = \frac{z-5}{-7}$$ $$\Rightarrow \frac{1}{2} = \frac{-3}{-3} = \frac{-7}{5}$$ Now normal of the plane will be perpendicular to the line, so using perpendicular condition we get, $$\therefore (2 + 5\lambda)(2) + (1 - 3\lambda)(4) + (4\lambda - 1)5 = 0$$ $$\Rightarrow 4 + 10\lambda + 4 - 12\lambda + 20\lambda - 5 = 0$$ $$\Rightarrow 18\lambda = -3 \Rightarrow \lambda = -\frac{1}{6}$$ So, equation of the Plane will be, $$P : \frac{7}{6}x + \frac{3}{2}y - \frac{5}{2}z - \frac{9}{2} = 0$$ $$\Rightarrow 7x + 9y - 10z - 27 = 0$$ Now to find $AB$, Let $\frac{x-8}{-3} = \frac{y+1}{4} = \frac{z+19}{12} = k$ So, the point $B = (-3k + 8, 4k - 1, 12k - 19)$ And $B$ lies on plane $P$. $$7(-3k + 8) + 9(4k - 1) - 10(12k - 19) = 27$$ $$\Rightarrow -21k + 56 + 36k - 9 - 120k + 190 = 27$$ $$\Rightarrow -105k = -210$$ $$\Rightarrow k = 2$$ $$\therefore B = (2, 7, 5)$$ Hence, Distance is $AB = \sqrt{36 + 64 + 576} = \sqrt{676} = 26$ Hence this is the required answer.

Question 24

Maths · Conic Sections · Fill in the blank

Let an ellipse with centre $(1, 0)$ and latus rectum of length $\frac{1}{2}$ have its major axis along x-axis. If its minor axis subtends an angle $60^\circ$ at the foci, then the square of the sum of the lengths of its minor and major axes is equal to .

Answer: 9

Solution

Given, An ellipse with centre $(1, 0)$ and latus rectum of length $\frac{1}{2}$ have its major axis along x-axis And its minor axis subtends an angle $60°$ at the foci. So, on plotting the diagram we get, Now from diagram we get, $\frac{b^2}{a} = \frac{1}{2} \Rightarrow b^2 = \frac{a}{2}$ ...(1) And $\tan 30° = \frac{b}{c}$ $\Rightarrow \left(\frac{1}{\sqrt{3}}\right) = \left(\frac{b}{c}\right)^2$ $\Rightarrow \frac{1}{3} = \frac{b^2}{c^2} = \frac{b^2}{a^2 - b^2}$ $\Rightarrow a^2 - b^2 = 3b^2$ $\Rightarrow b^2 = \frac{a^2}{4}$ .....(2) Now from equation (1) & (2) we get, $\Rightarrow a = 1, b^2 = \frac{1}{2}, b = \frac{1}{\sqrt{2}}$ Hence, $(2a + 2b)^2 = 9$

Question 25

Maths · Relations and Functions · Fill in the blank

Let $A = \{1, 2, 3, 4\}$ and $R$ be a relation on the set $A \times A$ defined by $R = \{((a, b), (c, d)): 2a + 3b = 4c + 5d\}$. Then the number of elements in $R$ is _________.

Answer: 6

Solution

Given, Set $A = \{1, 2, 3, 4\}$ and relation on $A \times A$ as $2a + 3b = 4c + 5d$. Now, maximum value of $2a + 3b = 20$ at $(4, 4)$ and minimum value of $4c + 5d = 9$ at $(1, 1)$. So, $4c + 5d$ can be equal to $9, 13, 14, 17, 18, 19$. Now $2a + 3b$ can be $9$ if $(a, b) = (3, 1) \Rightarrow (c, d) = (1, 1)$. Similarly, $2a + 3b$ can be $13$, if $(a, b) = (2, 3) \Rightarrow (c, d) = (2, 1)$. And $2a + 3b$ can be $14$, if $(a, b) = (4, 2)$ or $(1, 4)$ $\Rightarrow$ (c, d) = (1, 2)$. Similarly, $2a + 3b$ can be $17$, if $(a, b) = (4, 3) $\Rightarrow$ (c, d) = (3, 1)$. And $2a + 3b$ can be $18$ if $(a, b) = (3, 4) $\Rightarrow$ (c, d) = (2, 2)$. Hence, there are total $6$ elements which satisfy the given relation.

Question 26

Maths · Principle of Mathematical Induction · Fill in the blank

The number of elements in the set $\{ n \in \mathbb{N} : 10 \leq n \leq 100$ and 3^n - 3 is a multiple of 7 \} is ______.

Answer: 15

Solution

Given that $n \in [10, 100]$ and $n \in \mathbb{N}$. Let us take the values of $n = 1, 2, 3, \ldots$ and check whether $3^n - 3$ is divisible by 7 or not. $$3^1 - 3 = 0$$ is divisible by 7 $$3^2 - 3 = 3, \; 3 is not divisible by 7$$ $$3^6 = 7k + 1 is not divisible by 7$$ $$3^7 = 7\alpha + 3,$$ $$3^7 - 3 = 7\alpha is divisible by 7$$ Similarly $$3^{13} = (7k + 1)(7\alpha + 3)$$ $$= 7\beta + 3$$ $$3^{13} - 3 = 7\beta is divisible by 7$$ If we observe the pattern for $n = 1, 7, 13, 3^n - 3$ is divisible by 7. That means the series forms an AP with $d = 6$. Also $n \in [10, 100]$ The required progression is $13, 19, \ldots, a_n$ $$a_n = 13 + (n - 1)6$$ But $13 + (n - 1)6 < 100$ $$n < 15.5$$ $$n = 15 \in \mathbb{N}$$ Therefore, the required answer is 15.

Question 27

Maths · Three Dimensional Geometry · Numerical

If the line $x = y = z$ intersects the line $x \sin A + y \sin B + z \sin C - 18 = 0 = x \sin 2A + y \sin 2B + z \sin 2C - 9$, where $A, B, C$ are the angles of a triangle $ABC$, then $80 \left( \sin \frac{A}{2} \sin \frac{B}{2} \sin \frac{C}{2} \right)$ is equal to .

Answer: 5

Solution

Given, the line $x = y = z$ intersects the line $x \sin A + y \sin B + z \sin C - 18 = 0 = x \sin 2A + y \sin 2B + z \sin 2C - 9$. So, let $x = y = z = k$. Now putting the value in $x \sin A + y \sin B + z \sin C = 18$ we get, $$k(\sin A + \sin B + \sin C) = 18$$ Now we know that, if $A, B \& C$ are angles of triangle then $\sin A + \sin B + \sin C = 4 \cos \frac{A}{2} \cdot \cos \frac{B}{2} \cdot \cos \frac{C}{2}$. $$\Rightarrow k \left( 4 \cos \frac{A}{2} \cdot \cos \frac{B}{2} \cdot \cos \frac{C}{2} \right) = 18 \ldots (i)$$ Also $k(\sin 2A + \sin 2A + \sin 2A) = 9$. And similarly $\sin 2A + \sin 2A + \sin 2A = 4 \sin A \cdot \sin B \cdot \sin C$. $$\Rightarrow k(4 \sin A \cdot \sin B \cdot \sin C) = 9 \ldots \ldots (ii)$$ Now dividing equation (i) $\&$ (ii) we get, $$8 \sin \frac{A}{2} \cdot \sin \frac{B}{2} \cdot \sin \frac{C}{2} = \frac{9}{18}$$ $$\Rightarrow 80 \sin \frac{A}{2} \cdot \sin \frac{B}{2} \cdot \sin \frac{C}{2} = 5$$

Question 28

Maths · Applications of Integrals · Numerical

If the area bounded by the curve $2y^2 = 3x$, lines $x + y = 3$, $y = 0$ and outside the circle $(x - 3)^2 + y^2 = 2$ is $A$, then $4(\pi + 4A)$ is equal to _________.

Answer: 42

Solution

Given: $2y^2 = 3x$, $x + y = 3$ (slope is $-1$) and $(x - 3)^2 + y^2 = 2$. Now plotting the diagram of the above function we have, So, required area is $$A = \int_0^{\frac{3}{2}} \left(3 - y - \frac{2y^2}{3}\right) \, dy - \frac{\pi (\sqrt{2})^2 \times 45^\circ}{360^\circ}$$ $$\Rightarrow A = \left[3y - \frac{y^2}{2}\right]_0^{\frac{3}{2}} - \frac{2}{3} \left[y^3\right]_0^{\frac{3}{2}} - \frac{\pi}{4}$$ $$\Rightarrow A = \frac{21}{8} - \frac{\pi}{4}$$ So, $$A = \frac{1}{4} \left(\frac{21}{2} - \pi\right)$$ $$\Rightarrow \pi + 4A = \frac{21}{2}$$ $$\Rightarrow 4(\pi + 4A) = 42$$

Question 29

Maths · Applications of Derivatives · Numerical

Consider the triangles with vertices $A(2, 1)$, $B(0, 0)$ and $C(t, 4)$, $t = [0, 4]$. If the maximum and the minimum perimeters of such triangles are obtained at $t = \alpha$ and $t = \beta$ respectively, then $6\alpha + 21\beta$ is equal to .

Answer: 48

Solution

Given, the triangles with vertices $A(2, 1)$, $B(0, 0)$ and $C(t, 4)$, $t = [0, 4]$. And the maximum and the minimum perimeters of such triangles are obtained at $t = \alpha$ and $t = \beta$ respectively. Now to minimise $CA + CB$, in the below diagram take the image of $B$ in $y = 4$. We get, $B' = (0, 8)$. Now finding the equation of $AB'$ we get, $$y - 8 = -\frac{7}{2}(x - 0)$$ Now, putting $y = 4$ in the above equation we get, $$-4 = -\frac{7}{2}(x)$$ $$\Rightarrow x = \frac{8}{7} \Rightarrow \beta = \frac{8}{7}$$ Now, the maximum perimeter will be possible if $\alpha = 0$ or $4$. Now taking $\alpha = 0$ we get, $$AB = \sqrt{5}, \ BC = 4 \ & \ AC = \sqrt{13}$$ Now when $\alpha = 4$ we get, $$AB = \sqrt{5}, \ BC = 4\sqrt{2} \ & \ AC = \sqrt{13}$$ Now on comparing the perimeter we get, the maximum perimeter at $\alpha = 4$. Hence, $6\alpha + 21\beta = 48$.

Question 30

Maths · Integrals · Numerical

Let $f(x) = \int \frac{dx}{(3+4x^2)\sqrt{4-3x^2}}, \; |x| 0$, then $\alpha^2 + \beta^2$ is equal to ______.

Answer: 28

Solution

Given, $$f(x) = \int \frac{dx}{(3 + 4x^2) \sqrt{4 - 3x^2}}$$ Put $x = \frac{1}{t}$, $dx = -\frac{1}{t^2} dt$ So, $$f(x) = -\int \frac{-dt}{t^2 \left(3 + \frac{4}{t^2}\right) \sqrt{4 - \frac{3}{t^2}}}$$ $$\Rightarrow f(x) = \int \frac{1}{(3t^2 + 4) \sqrt{4t^2 - 3}} \, dt$$ Now let, $4t^2 - 3 = \lambda^2 \Rightarrow 8t \, dt = 2\lambda \, d\lambda$ $$\Rightarrow f(x) = -\int \frac{\lambda \, d\lambda}{4 \left(3 \left(\frac{\lambda^2 + 3}{4}\right) + 4\right) \lambda}$$ $$\Rightarrow f(x) = -\int \frac{\lambda \, d\lambda}{3\lambda^2 + 9 + 16}$$ $$\Rightarrow f(x) = -\int \frac{\lambda \, d\lambda}{\lambda^2 + 25}$$ $$\Rightarrow f(x) = -\frac{1}{3} \int \frac{\lambda \, d\lambda}{\lambda^2 + \left(\frac{25}{3}\right)}$$ $$\Rightarrow f(x) = -\frac{1}{3} \times \frac{\sqrt{3}}{5} \tan^{-1} \left(\frac{\sqrt{3}}{5}\right) + C$$ $$\Rightarrow f(x) = -\frac{\sqrt{3}}{15} \tan^{-1} \left(\frac{\sqrt{3}(4 - 3x^2)}{5x}\right) + C$$ Now using, $f(0) = 0 \Rightarrow c = + \frac{\sqrt{3}\pi}{30}$ Hence, $$f(1) = -\frac{\sqrt{3}}{15} \tan^{-1} \left(\frac{\sqrt{3}}{5}\right) + \frac{\sqrt{3}}{15} \times \frac{\pi}{2}$$ $$\Rightarrow f(1) = \frac{\sqrt{3}}{15} \left(\tan^{-1} \left(\frac{\sqrt{3}}{5}\right) - \frac{\pi}{2}\right)$$ $$\Rightarrow f(1) = \frac{\sqrt{3}}{15} \left(\frac{\pi}{2} - \tan^{-1} \left(\frac{\sqrt{3}}{5}\right)\right)$$ $$\Rightarrow f(1) = \frac{\sqrt{3}}{15} \tan^{-1} \left(\frac{\sqrt{3}}{5}\right)$$ $$\Rightarrow f(1) = \frac{1}{\sqrt{3}} \tan^{-1} \left(\frac{5}{\sqrt{3}}\right)$$ $$\Rightarrow f(1) = \frac{1}{\sqrt{3}} \tan^{-1} \left(\frac{5}{\sqrt{3}}\right)$$ Now comparing with given value of $f(1)$ we get, $\alpha = 5$ and $\beta = \sqrt{3}$ $$\Rightarrow \alpha^2 + \beta^2 = 28$$

Physics

Question 31

Physics · Electric Charges and Fields · Single correct

The electric field due to a short electric dipole at a large distance $(r)$ from center of dipole on the equatorial plane varies with distance as:

  1. $r$
  2. $\frac{1}{r^2}$
  3. $\frac{1}{r^3}$
  4. $\frac{1}{r}$

Answer: (c)

Solution

An electric dipole is a system of two charges of equal and opposite magnitude placed at a short distance. The dipole moment is, $p = 2ql$. The electric field due to the dipole is, $$E = \frac{2kp}{r^3}$$ Clearly, the electric field varies as $\frac{1}{r^3}$.

Question 32

Physics · Oscillations · Multiple correct

In a linear Simple Harmonic Motion (SHM) (A) Restoring force is directly proportional to the displacement. (B) The acceleration and displacement are opposite in direction. (C) The velocity is maximum at mean position. (D) The acceleration is minimum at extreme points. Choose the correct answer from the options given below:

  1. (A),(C) and (D) only
  2. (C) and (D) only
  3. (A), (B) and (C) only
  4. (A), (B) and (D) only

Answer: (c)

Solution

The equations of SHM is given by $$F = -kx$$ $$\Rightarrow a = -\omega^2 x$$ Velocity is given by, $v = \omega \sqrt{A^2 - x^2}$. Clearly, velocity is maximum at mean position and acceleration is maximum at extreme positions. Hence, this is the correct option.

Question 33

Physics · Gravitation · Single correct

Two identical particles each of mass $m$ go round a circle of radius $a$ under the action of their mutual gravitational attraction. The angular speed of each particle will be:

  1. $\sqrt{\frac{Gm}{a^3}}$
  2. $\sqrt{\frac{Gm}{8a^3}}$
  3. $\sqrt{\frac{Gm}{4a^3}}$
  4. $\sqrt{\frac{Gm}{2a^3}}$

Answer: (c)

Solution

The gravitational force ($F_G$) between the particles is given by $$F_G = \frac{Gm^2}{(2a)^2}$$ $$= \frac{Gm^2}{4a^2} \ldots (1)$$ The centripetal force ($F_C$) of each particle can be written as $$F_C = m\omega^2 a \ldots (2)$$ Under balanced condition, equate equation (1) and equation (2) and simplify to obtain the angular speed of each particle. $$m\omega^2 a = \frac{Gm^2}{4a^2}$$ $$\Rightarrow \omega^2 = \frac{Gm}{4a^3}$$ $$\Rightarrow \omega = \sqrt{\frac{Gm}{4a^3}}$$

Question 34

Physics · Communication Systems · Single correct

The height of transmitting antenna is 180 m and the height of the receiving antenna is 245 m. The maximum distance between them for satisfactory communication in line of sight will be: (given $R = 6400 \, \mathrm{km}$)

  1. 96 km
  2. 56 km
  3. 48 km
  4. 104 km

Answer: (d)

Solution

The maximum distance for line of sight communication is $$d = \sqrt{2hR} + \sqrt{2h'R}$$ The given data is $$R = 6400 \, \mathrm{km}$$ $$h = 180 \, \mathrm{m}$$ $$h' = 245 \, \mathrm{m}$$ Thus, the value is $$d = \sqrt{2 \times 180 \times 6400 \times 10^3} + \sqrt{2 \times 245 \times 6400 \times 10^3}$$ $$= 6 \times 80 \times 10^2 + 7 \times 80 \times 10^2$$ $$= 104 \, \mathrm{km}$$

Question 35

Physics · Nuclei · Single correct

The half-life of a radioactive nucleus is 5 years. The fraction of the original sample that would decay in 15 years is :

  1. $\frac{1}{8}$
  2. $\frac{1}{4}$
  3. $\frac{7}{8}$
  4. $\frac{3}{4}$

Answer: (c)

Solution

The formula to calculate the number of half lives covered by the radioactive material is given by $$n = \frac{t}{T_{\frac{1}{2}}} \ldots (1)$$ Substitute the values of the known parameters into equation (1) to calculate the number of half lives covered. $$n = \frac{15 \, years}{5 \, years}$$ $$= 3$$ The relation between the amount of radioactive substance after certain time can be written as $$N = N_0 2^{-n} \ldots (2)$$ Substitute the value of $n$ into equation (2) to obtain the fraction of the remaining substance. $$N = N_0 2^{-3}$$ $$\Rightarrow \frac{N}{N_0} = \frac{1}{8}$$ Hence, the amount of the decayed substance can be written as $$1 - \frac{N}{N_0} = 1 - \frac{1}{8}$$ $$= \frac{7}{8}$$

Question 36

Physics · Dual Nature of Radiation and Matter · Single correct

The de Broglie wavelength of an electron having kinetic energy $E$ is $\lambda$. If the kinetic energy of electron becomes $\frac{E}{4}$, then its de-Broglie wavelength will be:

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

Answer: (d)

Solution

The de-Broglie wavelength in the first case is $$\lambda = \frac{h}{\sqrt{2mE}}$$ In the second case the kinetic energy is $K = \frac{E}{4}$. Let the de-Broglie wavelength be $\lambda'$. The value of wavelength is $$\lambda' = \frac{h}{\sqrt{2m \frac{E}{4}}} = \frac{2h}{\sqrt{2mE}} = 2\lambda$$

Question 37

Physics · Current Electricity · Single correct

For designing a voltmeter of range 50 V and an ammeter of range 10 mA using a galvanometer which has a coil of resistance 54 Ω showing a full scale deflection for 1 mA as in figure.

  1. and (C)
  2. and (E)
  3. and (D)
  4. and (B)

Answer: (a)

Solution

The resistance is given by $$R = \frac{V}{I_g} - G$$ $$\Rightarrow \frac{50}{10^{-3}} - 54 \approx 50 \, \mathrm{k\Omega}$$ For ammeter, $$S = \frac{I_g G}{I - I_g}$$ $$\Rightarrow S = \frac{10^{-3} \times 54}{(10 - 1) \times 10^{-3}} = 6 \, \Omega$$

Question 38

Physics · Kinetic Theory · Single correct

A flask contains Hydrogen and Argon in the ratio 2 : 1 by mass. The temperature of the mixture is $30^\circ \mathrm{C}$. The ratio of average kinetic energy per molecule of the two gases $\left( \frac{K_{\mathrm{argon}}}{K_{\mathrm{hydrogen}}} \right)$ is: (Given : Atomic Weight of $\mathrm{Ar} = 39.9$)

  1. 2
  2. 1
  3. 39.9
  4. $\frac{39.9}{2}$

Answer: (b)

Solution

The formula to calculate the average kinetic energy per molecule of a gas at any temperature $T$ is given by $$K_{avg} = \frac{3}{2} k_B T$$ where, $k_B$ is Boltzmann constant. From above equation, it can be concluded that the average kinetic energy per molecule is independent of the molecular weight of the gas. Hence, the required ratio is 1 : 1.

Question 39

Physics · Current Electricity · Single correct

Given below are two statements: Statement I : The equivalent resistance of resistors in a series combination is smaller than least resistance used in the combination. Statement II : The resistivity of the material is independent of temperature. In the light of the above statements, choose the correct answer from the options given below:

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

Answer: (a)

Solution

The formula for series equivalent resistance is given by $R_s = R_1 + R_2 + \ldots + R_n$ Hence, the equivalent resistance will be the highest value compared to other resistances. The resistivity of a material is given by, $\rho = \rho_0 [1 + \alpha \Delta T]$ Clearly, the resistivity is dependent on temperature. Hence, option (1) is correct.

Question 40

Physics · Work, Energy and Power · Single correct

A body is released from a height equal to the radius $(R)$ of the earth. The velocity of the body when it strikes the surface of the earth will be: (Given $g$ = acceleration due to gravity on the earth.)

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

Answer: (b)

Solution

Using conservation of mechanical energy, $$U_i + K_i = U_f + K_f$$ $$\Rightarrow -\frac{GMm}{2R} + 0 = -\frac{GMm}{R} + \frac{1}{2}mv^2$$ $$\Rightarrow \frac{1}{2}mv^2 = \frac{GMm}{2R}$$ $$\Rightarrow v = \sqrt{\frac{GM}{R}} = \sqrt{gR}$$

Question 41

Physics · Electromagnetic Induction · Single correct

A 12 $\,$ $\mathrm{V}$ battery connected to a coil of resistance 6 $\,$ $\Omega$ through a switch, drives a constant current in the circuit. The switch is opened in 1 $\,$ $\mathrm{ms}$. The emf induced across the coil is 20 $\,$ $\mathrm{V}$. The inductance of the coil is :

  1. 10 $\,$ $\mathrm{mH}$
  2. 8 $\,$ $\mathrm{mH}$
  3. 5 $\,$ $\mathrm{mH}$
  4. 12 $\,$ $\mathrm{mH}$

Answer: (a)

Solution

The current $(i)$ through the circuit is given by $$i = \frac{V}{R}$$ $$= \frac{12 \, \mathrm{V}}{6 \, \Omega}$$ $$= 2 \, \mathrm{A}$$ The formula to calculate the induced emf in the coil can be written as $$\varepsilon = L \frac{di}{dt} \ldots (1)$$ Substitute the values of the known parameters into equation (1) and solve to calculate the inductance of the coil. $$20 \, \mathrm{V} = L \times \frac{2 \, \mathrm{A}}{1 \times 10^{-3} \, \mathrm{s}}$$ $$\Rightarrow L = \frac{20 \, \mathrm{V} \times 1 \times 10^{-3} \, \mathrm{s}}{2 \, \mathrm{A}}$$ $$= 10 \, \mathrm{mH}$$

Question 42

Physics · Mechanical Properties of Solids · Single correct

A wire of length $L$ and radius $r$ is clamped rigidly at one end. When the other end of the wire is pulled by a force $f$, its length increases by $l$. Another wire of same material of length $2L$ and radius $2r$ is pulled by a force $2f$. Then the increase in its length will be:

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

Answer: (d)

Solution

Young's modulus is same for both the wires since the material is same. For the first wire, $$Y = \frac{fL}{\pi r^2 l} \cdots (i)$$ For the second wire, $$Y = \frac{2f(2L)}{4\pi r^2 l'} \cdots (ii)$$ Dividing (i) by (ii) $$\frac{fL}{\pi r^2 l} \times \frac{4\pi r^2 l'}{4fL} = 1$$ $$\Rightarrow l' = l$$

Question 43

Physics · Motion in a Straight Line · Single correct

The position of a particle related to time is given by $x = (5t^2 - 4t + 5) \, \mathrm{m}$. The magnitude of velocity of the particle at $t = 2 \, \mathrm{s}$ will be :

  1. 06 $\mathrm{m \, s^{-1}}$
  2. 14 $\mathrm{m \, s^{-1}}$
  3. 10 $\mathrm{m \, s^{-1}}$
  4. 16 $\mathrm{m \, s^{-1}}$

Answer: (d)

Solution

It is given that $x = 5t^2 - 4t + 5$ The velocity is given by $$v = \frac{dx}{dt} = \frac{d(5t^2 - 4t + 5)}{dt} = 10t - 4$$ At $t = 2 \, \mathrm{s}$, $$v = 10(2) - 4 = 16 \, \mathrm{m \, s^{-1}}$$

Question 44

Physics · Laws of Motion · Single correct

The position vector of a particle related to time $t$ is given by $\vec{r} = (10t\hat{i} + 15t^2\hat{j} + 7\hat{k}) \, \mathrm{m}$. The direction of net force experienced by the particle is:

  1. Positive $x$-axis
  2. In $x - y$ plane
  3. Positive $y$-axis
  4. Positive $z$-axis

Answer: (c)

Solution

Given, the position vector of the particle is $\vec{r} = 10t \hat{i} + 15t^2 \hat{j} + 7 \hat{k}$. The velocity of the particle can be calculated as follows: $$\vec{v} = \frac{d\vec{r}}{dt}$$ $$= \frac{d}{dt} \left( 10t \hat{i} + 15t^2 \hat{j} + 7 \hat{k} \right)$$ $$= 10 \hat{i} + 30t \hat{j}$$ And, the acceleration of the particle is given by $$\vec{a} = \frac{d\vec{v}}{dt}$$ $$= \frac{d}{dt} \left( 10 \hat{i} + 30t \hat{j} \right)$$ $$= 30 \hat{j}$$ Hence, the force on the particle can be written as $$\vec{F} = m \vec{a}$$ $$= 30m \hat{j}$$

Question 45

Physics · Electromagnetic Waves · Single correct

Match List-I with List II of Electromagnetic waves with corresponding wavelength range: Choose the correct answer from the options given below:

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

Answer: (a)

Solution

The electromagnetic spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out with different energies. In daily life, two commonly known EM waves are the light wave and the radio wave. The other types of EM radiation that make up the electromagnetic spectrum are microwaves, infrared light, ultraviolet light, X-rays and gamma-rays. The wavelengths of different parts of the electromagnetic spectrum are related by the following relation: $$\lambda_X < \lambda_{\mathrm{UV}} < \lambda_{\mathrm{IR}} < \lambda_{\mathrm{MW}}$$

Question 46

Physics · Mathematics in Physics · Single correct

A vector in $x-y$ plane makes an angle of $30^\circ$ with $y$-axis. The magnitude of $y$-component of vector is $2\sqrt{3}$. The magnitude of $x$-component of the vector will be:

  1. $\frac{1}{\sqrt{3}}$
  2. 6
  3. 2
  4. $\sqrt{3}$

Answer: (c)

Solution

The angle made by the vector on the $x$ axis is $\theta = 90^\circ - 30^\circ = 60^\circ$. Let the vector be $\vec{a}$. It is given that $$a_y = 2\sqrt{3}$$ $$\Rightarrow a \sin 60^\circ = 2\sqrt{3}$$ $$\Rightarrow \frac{a \sqrt{3}}{2} = 2\sqrt{3}$$ $$\Rightarrow a = 4$$ The $x$ component is $$a_x = a \cos 60^\circ$$ $$\Rightarrow a_x = 4 \times \frac{1}{2} = 2$$

Question 47

Physics · Physical World, Units and Measurements · Single correct

The speed of a wave produced in water is given by $\nu = \lambda^a g^b \rho^c$. Where $\lambda$, $g$ and $\rho$ are wavelength of wave, acceleration due to gravity and density of water respectively. The values of $a$, $b$ and $c$ respectively, are

  1. 1, -1, 0
  2. $\frac{1}{2}$, 0, $\frac{1}{2}$
  3. 1, 1, 0
  4. $\frac{1}{2}$, $\frac{1}{2}$, 0

Answer: (d)

Solution

The dimensional form of velocity can be written as $[v] = [\lambda^a g^b \rho^c]$. Therefore, $$[M^0 L T^{-1}] = [L]^a [L T^{-2}]^b [M L^{-3}]^c$$ Comparing the exponents for $M, L, T$, For $M$, $$M^c = M^0$$ For $L$, $$L^{a+b-3c} = L^1$$ For $T$, $$T^{-2b} = T^{-1}$$ So, $$c = 0 \ldots (i)$$ $$a + b - 3c = 1 \ldots (ii)$$ $$-2b = -1 \ldots (iii)$$ From equations (i), (ii), (iii), $$a = \frac{1}{2}, b = \frac{1}{2}, c = 0$$

Question 48

Physics · Thermodynamics · Single correct

A thermodynamic system is taken through cyclic process. The total work done in the process is :

  1. 200 $\mathrm{J}$
  2. 300 $\mathrm{J}$
  3. 100 $\mathrm{J}$
  4. Zero

Answer: (b)

Solution

The work done is given by the area of the $PV$ graph of the loop. $$W = \frac{1}{2} (V_E - V_C)(P_D - P_C) = \frac{2 \times 300}{2} \, \mathrm{J}$$ $$= 300 \, \mathrm{J}$$

Question 49

Physics · Wave Optics · Single correct

A single slit of width $a$ is illuminated by a monochromatic light of wavelength $600 \, \mathrm{nm}$. The value of $a$ for which first minimum appears at $\theta = 30^\circ$ on the screen will be:

  1. $1.2 \, \mu \mathrm{m}$
  2. $3 \, \mu \mathrm{m}$
  3. $1.8 \, \mu \mathrm{m}$
  4. $0.6 \, \mu \mathrm{m}$

Answer: (a)

Solution

For the first minima $a \sin \theta = \lambda$ The given data is $\theta = 30^\circ$ $\lambda = 600 \, \mathrm{nm}$ The value of $a$ is $$a = \frac{\lambda}{\sin 30^\circ} = \frac{600 \times 10^{-9}}{\frac{1}{2}} = 1.2 \, \mu \mathrm{m}$$

Question 50

Physics · Current Electricity · Single correct

In the given circuit, the current $I$ through the battery will be

  1. 2.5 $\mathrm{A}$
  2. 1 $\mathrm{A}$
  3. 2 $\mathrm{A}$
  4. 1.5 $\mathrm{A}$

Answer: (d)

Solution

In the first circuit diagram, the diodes $D_1$ and $D_3$ are forward biased and $D_2$ is reverse biased (hence, no current through it). So the circuit is simplified to the second diagram. Hence, the equivalent resistance is $$R_{eq} = \frac{20 \times 10}{20 + 10}$$ $$\Rightarrow R_{eq} = \frac{20}{3} \, \Omega$$ Using Ohm's law, the current is $$I = \frac{10}{\frac{20}{3}} = \frac{30}{20} \, \mathrm{A} = 1.5 \, \mathrm{A}$$

Question 51

Physics · Electromagnetic Induction · Numerical

A 20 $\,$ $\mathrm{cm}$ long metallic rod is rotated with 210 $\,$ $\mathrm{rpm}$ about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field 0.2 $\,$ $\mathrm{T}$ parallel to the axis exists everywhere. The emf developed between the centre and the ring is $\,$ $\mathrm{mV}$. (Take $\pi$ = $\frac{22}{7}$)

Answer: 88

Solution

The data given is $\omega = 210 \times \frac{2\pi}{60} \, \mathrm{rad} \, \mathrm{s}^{-1} = 7\pi \, \mathrm{rad} \, \mathrm{s}^{-1}$, $l = 0.2 \, \mathrm{m}$, $B = 0.2 \, \mathrm{T}$. The emf is given by $$\varepsilon = \frac{B \omega l^2}{2}$$ $$= 0.2 \times 7\pi \times \frac{(0.2)^2}{2}$$ $$= 88 \, \mathrm{mV}$$

Question 52

Physics · Current Electricity · Fill in the blank

A network of four resistances is connected to 9 $\mathrm{V}$ battery, as shown in figure. The magnitude of voltage difference between the points $A$ and $B$ is _________ V.

Answer: 0

Solution

The resistance in each branch is $6 \, \Omega$. They are in parallel. So, net resistance is $R' = \frac{6}{2} = 3 \, \Omega$. The total current flowing through the loop, $$I = \frac{V}{R'} = \frac{9 \, \mathrm{V}}{3 \, \Omega} = 3 \, \mathrm{A}$$ Thus, through each branch the current is $1.5 \, \mathrm{A}$. Hence, the voltage difference across the points is $$V_A - V_B = (4 \times 1.5) - (2 \times 1.5) = 3 \, \mathrm{V}$$

Question 53

Physics · Waves · Numerical

The fundamental frequency of vibration of a string between two rigid support is 50 Hz. The mass of the string is 18 g and its linear mass density is 20 g m^{-1}. The speed of the transverse waves so produced in the string is ______ m s^{-1}.

Answer: 90

Solution

The fundamental frequency is $f = 50 \, \mathrm{Hz}$. The length of the string is $l = \frac{\lambda}{2}$. Linear mass density is $\mu = \frac{m}{l} = 20 \, \mathrm{g \, m^{-1}}$. Using $v = f \lambda$ $$\frac{v}{2l} = 50$$ $$\Rightarrow v = 100 \times l = \frac{100 \times 18}{20} = 90 \, \mathrm{m \, s^{-1}}$$

Question 54

Physics · Atoms · Numerical

As per given figure $A$, $B$ and $C$ are the first, second and third excited energy levels of hydrogen atom respectively. If the ratio of the two wavelengths (i.e. $\frac{\lambda_1}{\lambda_2}$) is $\frac{7}{4n}$, then the value of $n$ will be

Answer: 5

Solution

For $\lambda_1$ $$\frac{1}{\lambda_1} = RZ^2 \left( \frac{1}{2^2} - \frac{1}{3^2} \right) = R \left( \frac{5}{36} \right) \cdots (i)$$ For $\lambda_2$ $$\frac{1}{\lambda_2} = RZ^2 \left( \frac{1}{3^2} - \frac{1}{4^2} \right) = R \left( \frac{7}{144} \right) \cdots (ii)$$ Dividing (ii) by (i) $$\frac{\lambda_1}{\lambda_2} = \frac{7}{\frac{144}{5}} = \frac{7}{20}$$ So, $$\frac{7}{4n} = \frac{7}{20}$$ $$\Rightarrow n = 5$$

Question 55

Physics · System of Particles and Rotational Motion · Numerical

A solid sphere and a solid cylinder of same mass and radius are rolling on a horizontal surface without slipping. The ratio of their radius of gyrations respectively $(k_{sph} : k_{cyl})$ is $2 : \sqrt{x}$. The value of $x$ is _______.

Answer: 5

Solution

Considering rotational axis as the diametrical axis for sphere and axis of cylinder. Then $$K_1^2 = \frac{2}{5} R^2 and K_2^2 = \frac{1}{2} R^2$$ Therefore, $$\frac{K_1}{K_2} = \sqrt{\frac{2/5}{1/2}} = \sqrt{\frac{4}{5}}$$ Thus, $$\frac{K_1}{K_2} = \frac{2}{\sqrt{5}}$$ Comparing it with the given value in the question, $$\frac{2}{\sqrt{5}} = \frac{2}{\sqrt{x}}$$ Therefore, $x = 5$

Question 56

Physics · Ray Optics and Optical Instruments · Numerical

The refractive index of a transparent liquid filled in an equilateral hollow prism is $\sqrt{2}$. The angle of minimum deviation for the liquid will be ______ $^{\circ}$.

Answer: 30

Solution

For minimum deviation in a prism, $$\mu = \frac{\sin \left( \frac{D_{min} + A}{2} \right)}{\sin \frac{A}{2}}$$ The value of minimum deviation is $$\Rightarrow \sqrt{2} = \frac{\sin \left( \frac{D_{min} + 60^\circ}{2} \right)}{\sin 30^\circ}$$ $$\Rightarrow \frac{1}{\sqrt{2}} = \sin \left( \frac{D_{min} + 60^\circ}{2} \right)$$ $$\Rightarrow 45^\circ = \left( \frac{D_{min} + 60^\circ}{2} \right)$$ $$\Rightarrow D_{min} = 30^\circ$$

Question 57

Physics · Moving Charges and Magnetism · Numerical

An electron in a hydrogen atom revolves around its nucleus with a speed of $6.76 \times 10^6 \, \mathrm{m \, s^{-1}}$ in an orbit of radius $0.52 \, \mathrm{\AA}$. The magnetic field produced at the nucleus of the hydrogen atom is ______ T.

Answer: 40

Solution

The magnetic field due to the electron is given by $$B = \frac{\mu_0 q v \sin 90^\circ}{4 \pi r^2}$$ The given data is $v = 6.76 \times 10^6 \, \mathrm{m \, s^{-1}}$ $r = 0.52 \times 10^{-10} \, \mathrm{m}$ Thus, the magnetic field is $$B = \frac{10^{-7} \times (1.6 \times 10^{-19}) \times (6.76 \times 10^6)}{0.52 \times 0.52 \times 10^{-20}} = 40 \, \mathrm{T}$$

Question 58

Physics · Mechanical Properties of Fluids · Numerical

There is an air bubble of radius 1.0 mm in a liquid of surface tension $0.075 \, \mathrm{N \, m^{-1}}$ and density $1000 \, \mathrm{kg \, m^{-3}}$ at a depth of 10 cm below the free surface. The amount by which the pressure inside the bubble is greater than the atmospheric pressure is ______ $\mathrm{Pa} (g = 10 \, \mathrm{m \, s^{-2}})$.

Answer: 1150

Solution

The pressure inside the bubble is given by $$\Delta P = P - P_0 = \rho gh + \frac{2T}{r}$$ The data given is $r = 10^{-3} \, \mathrm{m}$, $T = 0.075 \, \mathrm{N \, m^{-1}}$, $\rho = 1000 \, \mathrm{kg \, m^{-3}}$, $h = 10 \, \mathrm{cm}$. Therefore, the pressure in the bubble is $$\Delta P = (1000 \times 10 \times 10 \times 10^{-2}) + \frac{2 \times 0.075}{10^{-3}} = 1000 + 150 = 1150 \, \mathrm{Pa}$$

Question 59

Physics · Work, Energy and Power · Numerical

A block of mass 10 kg is moving along $x$-axis under the action of force $F = 5x$ N. The work done by the force in moving the block from $x = 2$ m to 4 m will be ______ J.

Answer: 30

Solution

Work done is $W = \int F \, dx$. It is given that $F = 5x \, \mathrm{N}$. So, work done is $$W = \int_2^4 5x \, dx = \left. \frac{5x^2}{2} \right|_2^4$$ $$\Rightarrow W = \frac{5(16 - 4)}{2} = 30 \, \mathrm{J}$$

Question 60

Physics · Electrostatic Potential and Capacitance · Fill in the blank

In the given figure the total charge stored in the combination of capacitors is 100 $\mu$$\mathrm{C}$. The value of 'x' is __________.

Answer: 5

Solution

All the capacitors are in parallel combination and therefore potential drop across each capacitor would be the same. Charge on the capacitor can be written as, $Q = CV$. The charge on $C_1$ is $Q_1 = 2 \times 10 = 20 \, \mu \mathrm{C}$. The charge on $C_2$ is $Q_2 = x \times 10 = 10x \, \mu \mathrm{C}$. The charge on $C_3$ is $Q_3 = 3 \times 10 = 30 \, \mu \mathrm{C}$. By the given data, $$C_1 + C_2 + C_3 = 100 \, \mu \mathrm{C}$$ $$\Rightarrow 10(2 + x + 3) = 100$$ $$\Rightarrow x = 5$$

Chemistry

Question 61

Chemistry · Co-ordination Compounds · Single correct

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

  1. (A)–(III), (B)–(I), $(C)$–(IV), (D)–(II)
  2. (A)–(IV), (B)–(I), $(C)$–(II), (D)–(III)
  3. (A)–(III), (B)–(IV), $(C)$–(II), (D)–(I)
  4. (A)–(II), (B)–(III), $(C)$–(IV), (D)–(I)

Answer: (a)

Solution

Orlon is a man-made polymer of acrylonitrile. Thus, its monomer is vinyl cyanide or Prop-2-ene-1-nitrile. Natural Rubber is obtained from latex which is a sap of a tree. Natural rubber is a polymer of isoprene. Teflon is made of a chemical compound named polytetrafluoroethylene (PTFE) which is a synthetic fluoropolymer. Nylon-6 is produced by ring-opening chain growth polymerisation of caprolactam in the presence of water vapour and an acid catalyst at the melt.

Question 62

Chemistry · Alcohols, Phenols and Ethers · Single correct

The product formed in the following multistep reaction is:

Answer: (c)

Solution

Hydroboration-oxidation of terminal alkenes give primary alcohols. Propene gives propanol. Propanol on oxidation with PCC gives propanal. Propanal undergo nucleophi magnesium bromide give 2-butanol.

Question 63

Chemistry · Environmental Chemistry · Single correct

The possibility of photochemical smog formation will be minimum at

  1. Srinagar, Jammu and Kashmir in January
  2. Kolkata in October
  3. Mumbai in May
  4. New-Delhi in August (Summer)

Answer: (a)

Solution

Photochemical smog is a mixture of pollutants that are formed when nitrogen oxides and volatile organic compounds (VOCs) react to sunlight, creating a brown haze above cities. It tends to occur more often in summer, because that is when we have the most sunlight. The average temperature of Kashmir in January is estimated to be $-3.6^\circ \mathrm{C}$ in Srinagar, $-11.8^\circ \mathrm{C}$ in Pahalgam, and $-10.4^\circ \mathrm{C}$ in Gulmarg as their minimum temperatures.

Question 64

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

Which one of the following is not an example of calcination?

  1. $\mathrm{CaCO_3}$ $\xrightarrow{\Delta}$ $\mathrm{CaO}$ + $\mathrm{CO_2}$
  2. $\mathrm{Fe_2O_3}$ $\cdot$ $\mathrm{xH_2O}$ $\xrightarrow{\Delta}$ $\mathrm{Fe_2O_3}$ + $\mathrm{xH_2O}$
  3. $\mathrm{2PbS}$ + $\mathrm{3O_2}$ $\xrightarrow{\Delta}$ $\mathrm{2PbO}$ + $\mathrm{2SO_2}$
  4. $\mathrm{CaCO_3}$ $\cdot$ $\mathrm{MgCO_3}$ $\xrightarrow{\Delta}$ $\mathrm{CaO}$ + $\mathrm{MgO}$ + $\mathrm{2CO_2}$

Answer: (c)

Solution

Calcination is a process in which ore is heated in the absence of air or air might be supplied in a limited quantity. Roasting involves the heating of ore lower than its melting point in the presence of air or oxygen. $$2\mathrm{PbS} + 3\mathrm{O}_2 \xrightarrow{\Delta} 2\mathrm{PbO} + 2\mathrm{SO}_2$$ The above reaction is an example of roasting. Rest all the reactions are heated in the absence of oxygen.

Question 65

Chemistry · Chemical Bonding and Molecular Structure · Single correct

Consider the following statement (A) $\mathrm{NF}_3$ molecules has a trigonal planar structure. (B) Bond Length of $\mathrm{N}_2$ is shorter than $\mathrm{O}_2$. (C ) Isoelectronic molecules or ions have identical bond order. (D) Dipole moment of $\mathrm{H}_2\mathrm{S}$ is higher than that of water molecule. Choose the correct answer from the options given below:

  1. (A) and (B) are correct
  2. (A) and (D) are correct
  3. (C ) and (D) are correct
  4. (B) and (C ) are correct

Answer: (d)

Solution

In NF$_3$, nitrogen is having three bond pairs and a lone pair, hence, it has pyramidal shape. The bond order of N$_2$ = 3, and the bond order of O$_2$ = 2. Bond length is inversely related to bond order. Hence, bond length of N$_2$ is shorter than O$_2$. Isoelectronic species have identical bond order. Dipole moment of H$_2$O is more than that of H$_2$S due to higher electronegativity of O.

Question 66

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

Consider the following sequence of reactions The product 'B' is

Answer: (c)

Solution

The reaction of aniline (aromatic amine) with nitrous acid results in the diazonium salt formation which is benzenediazonium chloride. When benzenediazonium chloride reacts with N,N-dimethylaniline at ice-cold condition, it gives p-dimethylaminoazobenzene. It is an example of coupling reaction.

Question 67

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

The number of $P - O - P$ bonds in $H_4P_2O_7$, $(HPO_3)_3$, and $P_4O_{10}$ are respectively

  1. 0, 3, 6
  2. 0, 3, 4
  3. 1, 2, 4
  4. 1, 3, 6

Answer: (d)

Solution

In $\mathrm{H_4P_2O_7}$, each phosphorus undergo $\mathrm{sp^3}$ hybridisation. It has one P-O-P linkage in it. In $(\mathrm{HPO_3})_3$, each phosphorus undergo $\mathrm{sp^3}$ hybridisation. It has three P-O-P linkages in it. In $\mathrm{P_4O_{10}}$, each phosphorus undergo $\mathrm{sp^3}$ hybridisation. It has six P-O-P linkages in it.

Question 68

Chemistry · Structure of Atom · Single correct

Given below are two statements Statement I : According to Bohr’s model of hydrogen atom, the angular momentum of an electron in a given stationary state is quantised. Statement II : The concept of electron in Bohr’s orbit, violates the Heisenberg uncertainty principle. In the light of the above statements, choose the most appropriate answer from the options given below

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

Answer: (b)

Solution

According to Bohr's postulates the angular momentum in stationary orbit is quantised and is equal to $n h / 2 \pi$, where $n$ is the principal quantum number of the orbit. Bohr's model of the atom assumes fixed orbits and trajectories for the electron. Simultaneously known orbits and trajectories violate the Heisenberg Uncertainty Principle.

Question 69

Chemistry · Hydrocarbons · Single correct

Decreasing order of reactivity towards electrophilic substitution for the following compounds is:

  1. d > a > e > c > b
  2. e > d > a > b > c
  3. a > d > e > b > c
  4. c > b > a > d > e

Answer: (b)

Solution

Reactivity of aromatic compounds towards electrophilic substitution depends on the electron density on benzene ring. Higher the electron density on benzene ring, more be the reactivity towards electrophilic substitution reaction. Hence, the correct decreasing order is $$NMe_2 > OCH_3 > CH_3 > H > CF_3$$

Question 70

Chemistry · Equilibrium · Multiple correct

Which of the following statement(s) is/are correct? (A) The pH of $1 \times 10^{-8} \, \mathrm{M}$ HCl solution is 8. (B) The conjugate base of $\mathrm{H}_2 \mathrm{PO}_4^{-}$ is $\mathrm{HPO}_4^{2-}$. $(C)$ $K_w$ increases with increase in temperature. (D) When a solution of a weak monoprotic acid is titrated against a strong base at half neutralisation point, pH $= \frac{1}{2} pK_a$. Choose the correct answer from the options given below:

  1. (B), $(C)$
  2. (A), (D)
  3. (A), (B), $(C)$
  4. (B), $(C)$, (D)

Answer: (a)

Solution

When concentration of $\mathrm{H}^+$ ion is more than $10^{-7} \, \mathrm{M}$, the proton concentration from water must be considered. Hence, the pH of $10^{-8} \, \mathrm{M}$ HCl solution is not equal to 8. $$\mathrm{H_2PO_4^-} \rightleftharpoons \mathrm{HPO_4^{2-}} + \mathrm{H^+}$$ $K_w$ increases with increase in temperature as dissociation of water increases with increase in temperature. When weak monoprotic acid is titrated against strong base, at half neutralization point, the solution becomes acidic buffer and its pH is given by $$\mathrm{pH} = \mathrm{p}K_a + \log \left( \frac{[Salt]}{[Acid]} \right)$$ $$\Rightarrow \mathrm{pH} = \mathrm{p}K_a + 0 as [salt] = [acid]$$

Question 71

Chemistry · The s-Block Elements · Single correct

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R ): Assertion (A): $\mathrm{BeCl_2}$ and $\mathrm{MgCl_2}$ produce characteristic flame. Reason (R ): The excitation energy is high in $\mathrm{BeCl_2}$ and $\mathrm{MgCl_2}$. In the light of the above statements, choose the correct answer from the options given below:

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

Answer: (d)

Solution

In Be and Mg, the electrons are strongly bound. The energy required to excite these electrons is very high. Therefore, when the electron reverts back to its original position, the energy released does not fall in the visible region. Hence, no colour in the flame is seen.

Question 72

Chemistry · Amines · Single correct

In the above conversion, the correct sequence of reagents to be added is

  1. $KMnO_4$, (ii) $Br_2$/Fe, (iii) Fe/$H^+$, (iv) $Cl_2$
  2. $Br_2$/Fe, (ii) Fe/$H^+$, (iii) $KMnO_4$, (iv) $Cl_2$
  3. Fe/$H^+$, (ii) HONO, (iii) CuCl, (iv) $KMnO_4$, (v) $Br_2$
  4. $Br_2$/Fe, (ii) Fe/$H^+$, (iii) HONO, (iv) CuCl, (v) $KMnO_4$

Answer: (d)

Solution

The required product can be obtained by the following method. In this method nitro toluene is subjected to bromination, bromo group is substituted at ortho position to the methyl as it is more activating group. Then nitro group is reduced to amino group with iron metal in acid. The amine group undergoes diazotisation with nitrous acid. The diazonium group is replaced with chloro group in the presence of cuprous chloride. Finally, methyl group is oxidised in the presence of potassium permanganate.

Question 73

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

'A' formed in the above reaction is

Answer: (a)

Solution

Aldehydes and ketones react with water to give 1,1-geminal diols known as hydrates. In general, hydrates are not stable enough to be isolated as the equilibrium shifts back to starting materials (due to Le Chatelier's principle). But the following ketone forms stable diol due to the formation of hydrogen bonding as shown below.

Question 74

Chemistry · Biomolecules · Single correct

Which is not true for arginine?

  1. It has a fairly high melting point
  2. It is associated with more than one $pK_a$ values.
  3. It has high solubility in benzene.
  4. It is a crystalline solid.

Answer: (c)

Solution

In aqueous solutions carboxyl group can lose protons and the amino group can accept a proton thus giving rise to a dipolar known as zwitter ion. Due to this dipolar behaviour they have strong electrostatic interactions within them. For this reason melting point of amino acids is high. It has more than one basic groups amine and guanidine, hence it has two pKa values. It is crystalline solid. Since arginine is polar, it is not soluble in benzene.

Question 75

Chemistry · Hydrogen · Single correct

During water-gas shift reaction

  1. Carbon monoxide is oxidized to carbon dioxide.
  2. Water is evaporated in presence of catalyst.
  3. Carbon is oxidized to carbon monoxide.
  4. Carbon dioxide is reduced to carbon monoxide.

Answer: (a)

Solution

The reaction between CO of syn gas and steam in presence of catalyst is called water gas shift reaction. $$\mathrm{CO + H_2O \rightarrow CO_2 + H_2O}$$ This reaction increases the yield of hydrogen obtained from coal gasification reaction as shown below. $$\mathrm{C + H_2O \rightarrow \underset{syn gas}{\mathrm{CO + H_2}}}$$

Question 76

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

For a good quality cement, the ratio of silica to alumina is found to be

  1. 1.5
  2. 4.5
  3. 2
  4. 3

Answer: (d)

Solution

For a good quality cement the ratio of silica ($\mathrm{SiO_2}$) and alumina ($\mathrm{Al_2O_3}$) should be between 2.5 to 4.0. Similarly, the ratio of lime ($\mathrm{CaO}$) to the total oxide mixtures consisting of $\mathrm{SiO_2}$, $\mathrm{Al_2O_3}$ and $\mathrm{Fe_2O_3}$ should be roughly 2 : 1 : 1. If lime is in excess, the cement cracks during setting.

Question 77

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

Which of the following statement is correct for paper chromatography?

  1. Water present in the pores of the paper forms the stationary phase.
  2. Paper sheet forms the stationary phase.
  3. Water present in the mobile phase gets absorbed by the paper which then forms the stationary phase.
  4. Paper and water present in its pores together form the stationary phase.

Answer: (a)

Solution

The principle of paper chromatography is partition. In paper chromatography there are two phases: one is the stationary phase and the other is the mobile phase. Here, water trapped in the paper acts as the stationary phase and solvent acts as the mobile phase.

Question 78

Chemistry · Haloalkanes and Haloarenes · Single correct

The major product formed in the Friedel-Craft acylation of chlorobenzene is

Answer: (d)

Solution

Friedel-Crafts acylation is a reaction in which the addition of an acyl group to an aromatic ring takes place. The reaction will lead to the aromatic ring being transformed into a ketone.

Question 79

Chemistry · Co-ordination Compounds · Single correct

The complex with highest magnitude of crystal field splitting energy ($\Delta_0$) is

  1. $[\mathrm{Ti(OH_2)_6}]^{3+}$
  2. $[\mathrm{Cr(OH_2)_6}]^{3+}$
  3. $[\mathrm{Mn(OH_2)_6}]^{3+}$
  4. $[\mathrm{Fe(OH_2)_6}]^{3+}$

Answer: (b)

Solution

Crystal field stabilisation energy of the complex can be calculated as follows, CFSE = number of $t_{2g}$ electrons $\($ $\times$ (-0.4) $\)$ + number of $e_g$ electrons $\($ $\times$ (0.6) $\)$ Complex $\hspace{1cm}$ CFSE $$[\mathrm{Ti(OH_2)_6}]^{3+} (t_{2g}^1 e_g^0) -0.4 \, \Delta_0$$ $$[\mathrm{Cr(H_2O)_6}]^{3+} (t_{2g}^3 e_g^0) -1.2 \, \Delta_0$$ $$[\mathrm{Mn(H_2O)_6}]^{3+} (t_{2g}^3 e_g^1) -0.6 \, \Delta_0$$ $$[\mathrm{Fe(H_2O)_6}]^{3+} (t_{2g}^3 e_g^2) 0$$

Question 80

Chemistry · The Solid State · Single correct

Which of the following expressions is correct in case of a CsCl unit cell (edge length 'a')?

  1. $r_{\mathrm{Cs}^+} + r_{\mathrm{Cl}^-} = \frac{a}{2}$
  2. $r_{\mathrm{Cs}^+} + r_{\mathrm{Cl}^-} = \frac{\sqrt{3}}{2} a$
  3. $r_{\mathrm{Cs}^+} + r_{\mathrm{Cl}^-} = \frac{a}{\sqrt{2}}$
  4. $r_{\mathrm{Cs}^+} + r_{\mathrm{Cl}^-} = a$

Answer: (b)

Solution

CsCl has body centered type structure in which $\mathrm{Cs}^+$ occupies at corner of a cube and $\mathrm{Cl}^-$ occupies the centre of the cube. $$2r_{\mathrm{Cs}^+} + 2r_{\mathrm{Cl}^-} = \sqrt{3}a (where a is the edge length of the cube)$$ $$r_{\mathrm{Cs}^+} + r_{\mathrm{Cl}^-} = \frac{\sqrt{3}}{2} a$$

Question 81

Chemistry · Co-ordination Compounds · Numerical

The homoleptic and octahedral complex of $\mathrm{Co}^{2+}$ and $\mathrm{H}_2\mathrm{O}$ has _____ unpaired electron(s) in the $t_{2g}$ set of orbitals.

Answer: 1

Solution

The electronic configuration of $\mathrm{Co^{2+}}$ is $3d^7$. In an octahedral complex of $\mathrm{Co^{2+}}$ with $\mathrm{H_2O}$ ligands, the $d$ orbitals split into two sets of energy levels: $t_{2g}$ (lower energy) and $e_g$ (higher energy). In this case, since the complex is octahedral, we have six ligands surrounding the central cobalt ion. Each ligand donates a pair of electrons to the cobalt ion, occupying the available $d$ orbitals. So, $$\left[ \mathrm{Co\ (H_2O)_6} \right]^{2+} = d^7 (High spin) = t_{2g}^5 e_g^2$$ In the $t_{2g}$ set of orbitals, there will be 1 unpaired electron.

Question 82

Chemistry · Co-ordination Compounds · Numerical

The volume (in mL) of 0.1 M $\mathrm{AgNO}_3$ required for complete precipitation of chloride ions present in 20 mL of 0.01 M solution of $[\mathrm{Cr} (\mathrm{H}_2\mathrm{O})_5 \mathrm{Cl}] \mathrm{Cl}_2$ as silver chloride is

Answer: 4

Solution

($\mathrm{Cr\ (H_2O)_5\ Cl}$)$\mathrm{Cl_2}$ $\rightarrow$ ($\mathrm{Cr\ (H_2O)_5\ Cl}$)^{+} + 2$\mathrm{Cl}$^{-} Number of ionisable $\mathrm{Cl}^{-}$ in $(\mathrm{Cr\ (H_2O)_5\ Cl})\mathrm{Cl_2}$ is 2. Molarity of $\mathrm{Cl}^{-}$ ions $= 0.01 \times 2 = 0.02\ \mathrm{M}$ Therefore, millimoles of $\mathrm{Cl}^{-}$ ions in the given solution $$= 20 \times 0.02$$ Therefore, millimoles of $\mathrm{AgNO_3}$ required $= 20 \times 0.2$ $$V \times 0.1 = 20 \times 0.02$$ $$V = 4\ \mathrm{mL}$$

Question 83

Chemistry · Redox Reactions · Numerical

The total change in the oxidation state of manganese involved in the reaction of $KMnO_4$ and potassium iodide in the acidic medium is _______.

Answer: 5

Solution

In the reaction of $\mathrm{KMnO_4}$ and potassium iodide (KI) in an acidic medium, the $\mathrm{KMnO_4}$ acts as an oxidizing agent, and the iodide ions ($\mathrm{I^-}$) in KI act as reducing agents. $$\mathrm{KMnO_4 + KI + H^+ \rightarrow Mn^{+2} + I_2 + H_2O}$$ In $\mathrm{KMnO_4}$, the oxidation state of manganese is $+7$, which is the highest possible oxidation state for manganese in this compound. In the final product, $\mathrm{MnSO_4}$, the oxidation state of manganese is $+2$. Therefore, the total change in the oxidation state of manganese is: $$+7 (initial) - +2 (final) = 5$$ Hence the change in O. S. of Mn is $5$.

Question 84

Chemistry · The d-and f-Block Elements · Fill in the blank

In Chromyl chloride, the oxidation state of chromium is (+) .

Answer: 6

Solution

The chemical formula of Chromyl chloride is $\mathrm{CrO_2Cl_2}$. The oxidation state of chromium in chromyl chloride ($\mathrm{CrO_2Cl_2}$) is $+6$. Let the oxidation number of Chromium be $x$, the oxidation state of oxygen is $-2$, the oxidation state of chlorine is $-1$. Then, $$x + 2(-2) + 2(-1) = 0$$ $$x - 6 = 0$$ $$x = 6$$

Question 85

Chemistry · Classification of Elements and Periodicity in Properties · Fill in the blank

The total number of isoelectronic species from the given set is _______. $\mathrm{O}^{2-}$, $\mathrm{F}^{-}$, $\mathrm{Al}$, $\mathrm{Mg}^{2+}$, $\mathrm{Na}^{+}$, $\mathrm{O}^{+}$, $\mathrm{Mg}$, $\mathrm{Al}^{3+}$, $\mathrm{F}$

Answer: 5

Solution

Isoelectronic are those which have the same number of electrons. Let us write the number of electrons from the given species. Hence five species among the given are isoelectronic species.

Question 86

Chemistry · Solutions · Numerical

The vapour pressure of $30\%$ (w/v) aqueous solution of glucose is $\_\_\_\_$ $\mathrm{mm\,Hg}$ at $25^\circ\mathrm{C}$. [Given: The density of $30\%$ (w/v) aqueous solution of glucose is $1.2\,\mathrm{g\,cm^{-3}}$ and the vapour pressure of pure water is $24\,\mathrm{mm\,Hg}$.] (Molar mass of glucose is $180\,\mathrm{g\,mol^{-1}}$)

Answer: 23

Solution

To calculate the vapour pressure of the 30% (w/v) aqueous solution of glucose, we can use Raoult's law, which states that the vapour pressure of a component in an ideal solution is directly proportional to its mole fraction in the solution. Weight of solution = $100 \times 1.2 = 120 \, \mathrm{gm}$ Weight of water = $120 - 30 = 90 \, \mathrm{gm}$ Now using formula $$\frac{P_0 - P}{P} = \frac{moles of glucose}{moles of water}$$ $$\frac{24 - P}{P} = \frac{30}{180} = \frac{3}{90}$$ $$24 \times 90 - P \times 90 = 3P$$ $$\Rightarrow P = 23.22$$

Question 87

Chemistry · Surface Chemistry · Numerical

$20 \, \mathrm{mL}$ of $0.5 \, \mathrm{M}$ NaCl is required to coagulate $200 \, \mathrm{mL}$ of $\mathrm{As_2S_3}$ solution in $2$ hours. The coagulating value of NaCl is _______ .

Answer: 50

Solution

Coagulating value $= \frac{\text{Millimoles of electrolyte}}{\text{Volume of sol in litre}}$. $20 \, \mathrm{ml}$ of $0.5 \, \mathrm{M}$ NaCl contains NaCl $= 20 \times 0.5 = 10$ milli moles. $200 \, \mathrm{ml}$ of $\mathrm{As_2S_3}$ required NaCl for the coagulation $= 10$ milli moles. $\therefore 1000 \, \mathrm{ml}$ of $\mathrm{As_2S_3}$ required NaCl for the coagulation $= 10 \times \frac{1000}{200} = 50$ milli moles.

Question 88

Chemistry · Chemical Kinetics and Nuclear Chemistry · Numerical

For a reversible reaction $A \rightleftharpoons B$, the $\Delta H$ forward reaction $= 20 \, \mathrm{kJ} \, \mathrm{mol}^{-1}$. The activation energy of the uncatalyzed forward reaction is $300 \, \mathrm{kJ} \, \mathrm{mol}^{-1}$. When the reaction is catalysed keeping the reactant concentration same, the rate of the catalysed forward reaction at $27^\circ \mathrm{C}$ is found to be same as that of the uncatalyzed reaction at $327^\circ \mathrm{C}$. The activation energy of the catalysed backward reaction is $\mathrm{kJ} \, \mathrm{mol}^{-1}$.

Answer: 130

Solution

As per the question, to determine the activation energy of the catalyzed backward reaction, we need to use the Arrhenius equation and the given information. The Arrhenius equation is given by: $$k = A e^{(-E_a / RT)}$$ $$A e^{-\frac{300 \times 10^3}{600 \times R}} = A e^{-\frac{E_a}{300 \times R}}$$ $$\Rightarrow \frac{10^3}{2} = \frac{E_a}{300}$$ $$\Rightarrow E_a = 150 \times 10^3 \, \mathrm{J} \, \mathrm{mol}^{-1}$$ $$\Rightarrow E_a = 150 \, \mathrm{kJ} \, \mathrm{mol}^{-1}$$ Therefore, the activation energy of the catalysed backward reaction is the energy of activation for the backward reaction, $E_b = E_a - \Delta H$. $$= 150 - 20 = 130 \, \mathrm{kJ} \, \mathrm{mol}^{-1}$$

Question 89

Chemistry · Electrochemistry · Single correct

The number of correct statements from the following is ________

  1. Conductivity always decreases with decrease in concentration for both strong and weak electrolytes.
  2. The number of ions per unit volume that carry current in a solution increases on dilution.
  3. Molar conductivity increases with decrease in concentration.
  4. The variation in molar conductivity is different for strong and weak electrolytes.
  5. For weak electrolytes, the change in molar conductivity with dilution is due to decrease in degree of dissociation.

Answer: (c)

Solution

Conductivity always decreases with the decrease in concentration both, for weak and strong electrolytes. This can be explained by the fact that the number of ions per unit volume that carry the current in a solution decreases on dilution. Molar conductivity of a strong and weak electrolyte increases with dilution. On dilution as volume of solution increases. Thus, on dilution, ions get more apart and mobility of ions increases which leads to increase in molar conductivity of the solution. Except (B) and (E), all statements are correct.

Question 90

Chemistry · Thermodynamics · Numerical

30.4 \, $\mathrm{kJ}$ of heat is required to melt one mole of sodium chloride and the entropy change at the melting point is 28.4 \, $\mathrm{J \, K^{-1} \, mol^{-1}}$ at 1 \, $\mathrm{atm}$. The melting point of sodium chloride is _______________ \, $\mathrm{K}$ (Nearest Integer)

Answer: 1070

Solution

The equilibrium process can be written as follows, $\mathrm{NaCl(s) \rightleftharpoons NaCl(l)}$ \[ \Delta S = \frac{\Delta H}{\text{Temp}} \] \[ T = \frac{\Delta H}{\Delta S} \] \[ = \frac{30.4 \times 10^3}{28.4} \] \[ = 1070.4 \, \mathrm{K} \]