JEE Main 29 January 2025 Shift 1 question paper with solutions

JEE Main 29 January 2025 Shift 1: all 75 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 · Conic Sections · Single correct

Let the line $x + y = 1$ meet the circle $x^2 + y^2 = 4$ at the points $A$ and $B$. If the line perpendicular to $AB$ and passing through the mid point of the chord $AB$ intersects the circle at $C$ and $D$, then the area of the quadrilateral $ADBC$ is equal to:

  1. 14
  2. 37
  3. 214
  4. 57

Answer: (c)

Solution

By solving $x = y$ with the circle, we get $C(\sqrt{2}, \sqrt{2})$ and $D(-\sqrt{2}, -\sqrt{2})$. By solving $x + y = 1$ with the circle $x^2 + y^2 = 4$, we set $$A \left( \frac{1 + \sqrt{7}}{2}, \frac{1 - \sqrt{7}}{2} \right)$$ & $$B \left( \frac{1 - \sqrt{7}}{2}, \frac{1 + \sqrt{7}}{2} \right)$$ Therefore, the area of quadrilateral $ACBD$ is $$= 2 \times Area of \triangle BCD$$ $$= 2 \times \frac{1}{2} \begin{vmatrix} \sqrt{2} & \sqrt{2} & 1 \\ \frac{1 - \sqrt{7}}{2} & \frac{1 + \sqrt{7}}{2} & 1 \\ -\sqrt{2} & -\sqrt{2} & 1 \end{vmatrix}$$ $$= 2\sqrt{14}$$

Question 2

Maths · Determinants · Single correct

Let M and m respectively be the maximum and the minimum values of $$f(x) = \begin{vmatrix} 1 + \sin^2 x & \cos^2 x & 4 \sin 4x \\ \sin^2 x & 1 + \cos^2 x & 4 \sin 4x \\ \sin^2 x & \cos^2 x & 1 + 4 \sin 4x \end{vmatrix}, \ x \in \mathbb{R}$$ Then $M^4 - m^4$ is equal to:

  1. 1280
  2. 1295
  3. 1215
  4. 1040

Answer: (a)

Solution

Given the matrix: $$\begin{vmatrix} 1 + \sin^2 x & \cos^2 x & 4 \sin 4x \\ \sin^2 x & 1 + \cos^2 x & 4 \sin 4x \\ \sin^2 x & \cos^2 x & 1 + 4 \sin 4x \end{vmatrix}, x \in \mathbb{R}$$ Perform the row operations: $$R_2 \to R_2 - R_1 \& R_3 \to R_3 - R_1$$ The matrix becomes: $$\begin{vmatrix} 1 + \sin^2 x & \cos^2 x & 4 \sin 4x \\ -1 & 1 & 0 \\ -1 & 0 & 1 \end{vmatrix}$$ Expand about $R_1$, we get $$f(x) = 2 + 4 \sin 4x$$ Thus, $M = max value of f(x) = 6$ $M = min value of f(x) = -2$ Therefore, $M^4 - M^4 = 1280$

Question 3

Maths · Conic Sections · Single correct

Two parabolas have the same focus $(4, 3)$ and their directrices are the $x$-axis and the $y$-axis, respectively. If these parabolas intersects at the points $A$ and $B$, then $(AB)^2$ is equal to:

  1. 392
  2. 384
  3. 192
  4. 96

Answer: (c)

Solution

The parabolas are $$(x - 4)^2 + (y - 3)^2 = x^2 \ldots (i)$$ and $$(x - 4)^2 + (y - 3)^2 = y^2 \ldots$$ If point of intersection are $A(x_1, y_1)$ and $B(x_2, y_2)$. By solving (i) and (ii), we get $$x_1 + x_2 = 14 and x_1 x_2 = 25$$ $$(AB)^2 = 2 \left( (x_1 + x_2)^2 - 4x_1 x_2 \right) = 192$$

Question 4

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

Let $ABC$ be a triangle formed by the lines $7x - 6y + 3 = 0$, $x + 2y - 31 = 0$ and $9x - 2y - 19 = 0$. Let the point $(h, k)$ be the image of the centroid of $\triangle ABC$ in the line $3x + 6y - 53 = 0$. Then $h^2 + k^2 + hk$ is equal to:

  1. 47
  2. 37
  3. 36
  4. 40

Answer: (b)

Solution

$\therefore$ centroid of $\triangle ABC =\left(\dfrac{9+3+5}{3},\dfrac{11+4+13}{3}\right) =\left(\dfrac{17}{3},\dfrac{28}{3}\right)$ Let image of centroid with respect to line mirror is $(h,k)$ $\therefore\; \left(\dfrac{k-\frac{28}{3}}{h-\frac{17}{3}}\right) \left(-\dfrac12\right) =-1 \qquad\cdots(1)$ $\left(\dfrac{h+\frac{17}{3}}{2}\right) + 6\left(\dfrac{k+\frac{28}{3}}{2}\right) =53 \qquad\cdots(2)$ Solving (1) \& (2) we get $h=3,\quad k=4$ $\therefore\;h^2+k^2+hk=37$

Question 5

Maths · Vector Algebra · Single correct

Let $\vec{a}=2\hat{i}-\hat{j}+3\hat{k}$, $\vec{b}=3\hat{i}-5\hat{j}+\hat{k}$ and $\vec{c}$ be a vector such that $\vec{a}\times\vec{c}=\vec{c}\times\vec{b}$ and $(\vec{a}+\vec{c})\cdot(\vec{b}+\vec{c})=168$. Then the maximum value of $|\vec{c}|^2$ is:

  1. 462
  2. 77
  3. 154
  4. 308

Answer: (d)

Solution

Given $\vec{a} = 2\hat{i} - \hat{j} + 3\hat{k}$ and $\vec{b} = 3\hat{i} - 5\hat{j} + 3\hat{k}$. We have $\vec{a} \times \vec{c} = \vec{c} \times \vec{b}$. Therefore, $\vec{a} \times \vec{c} + \vec{b} \times \vec{c} = 0$. This implies $(\vec{a} + \vec{b}) \times \vec{c} = 0$. Thus, $\vec{c} = \lambda(\vec{a} + \vec{b})$. So, $\vec{c} = \lambda(5\hat{i} - 6\hat{j} + 4\hat{k}) \ldots (1)$. The magnitude squared is $|\vec{c}|^2 = \lambda^2(25 + 36 + 16)$. Therefore, $|\vec{c}|^2 = 77\lambda^2$. The expression $(\vec{a} + \vec{c}) \cdot (\vec{b} + \vec{c}) = 168$ gives $\vec{a} \cdot \vec{b} + \vec{a} \cdot \vec{c} + \vec{c} \cdot \vec{b} + |\vec{c}|^2 = 168$. Simplifying, $14 + \vec{c} \cdot (\vec{a} + \vec{b}) + 77\lambda^2 = 168$. Using equation (1), $\lambda|5\hat{i} - 6\hat{j} + 4\hat{k}|^2 + 77\lambda^2 = 154$. This simplifies to $77\lambda + 77\lambda^2 - 154 = 0$. Solving $\lambda^2 + \lambda - 2 = 0$, we find $\lambda = -2, 1$. Therefore, the maximum value of $|\vec{c}|^2$ occurs when $\lambda = -2$. Thus, $|\vec{c}|^2 = 77\lambda^2 = 77 \times 4 = 308$.

Question 6

Maths · Permutations and Combinations · Single correct

Let P be the set of seven digit numbers with sum of their digits equal to 11. If the numbers in P are formed by using the digits 1, 2 and 3 only, then the number of elements in the set $P$ is:

  1. 173
  2. 164
  3. 158
  4. 161

Answer: (d)

Solution

(i) number of numbers created using 1111133 = $\($ $\frac{7!}{5!2!}$ $\Rightarrow$ 21 $\)$ (ii) number of numbers created using 1111223 = $\($ $\frac{7!}{4!2!}$ $\Rightarrow$ 105 $\)$ (iii) number of numbers created using 1112222 = $\($ $\frac{7!}{4!3!}$ $\Rightarrow$ 35 $\)$ Total = 161

Question 7

Maths · Applications of Integrals · Single correct

Let the area of the region \[ \left\{ (x,y): 2y\le x^2+3,\; y+|x|\le3,\; y\ge|x-1| \right\} \] be $A$. Then $6A$ is equal to:

  1. 16
  2. 12
  3. 14
  4. 18

Answer: (c)

Solution

Given that $A$ is the area of rectangle $ABDE$ minus the area of region $EDC$. $$A \Rightarrow 4 - 2 \int_{0}^{1} \left(3 - x\right) - \left(\frac{x^2 + 3}{2}\right) \, dx$$ $$A \Rightarrow 4 - 2 \left\{ 3x - \frac{x^2}{2} - \frac{x^3}{6} - \frac{3}{2}x \right\}_{0}^{1}$$ $$A \Rightarrow 4 - 2 \left\{ 3 - \frac{1}{2} - \frac{1}{6} - \frac{3}{2} \right\} = \frac{7}{3}$$ So $6A = 14$

Question 8

Maths · Binomial Theorem · Single correct

The least value of $n$ for which the number of integral terms in the Binomial expansion of $\left( \sqrt[3]{7} + \sqrt[12]{11} \right)^n$ is 183, is:

  1. 2184
  2. 2196
  3. 2148
  4. 2172

Answer: (a)

Solution

General term = $\binom{n}{r} \left\{ 7^{1/3} \right\}^{n-r} \left( 11^{1/12} \right)^r$ $$= \binom{n}{r} \left\{ 7 \right\}^{\frac{n-r}{3}} (11)^{r/12}$$ For integral terms, $r$ must be a multiple of 12. Therefore, $r = 12k$, $k \in \mathbb{W}$. Total values of $r = 183$. Hence $\max \, r = 12(182) = 2184$. Min value of $n = 2184$.

Question 9

Maths · Complex Numbers and Quadratic Equations · Single correct

The number of solutions of the equation ($\frac{9}{x}$ - $\frac{9}{\sqrt{x}}$ + 2 ) ( $\frac{2}{x}$ - $\frac{7}{\sqrt{x}}$ + 3) = 0 is:

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

Answer: (d)

Solution

Consider $\frac{1}{\sqrt{x}} = \alpha$ where $x > 0$. $$\{9\alpha^2 - 9\alpha + 2\}\{2\alpha^2 - 7\alpha + 3\} = 0$$ $$(3\alpha - 2)(3\alpha - 1)(\alpha - 3)(2\alpha - 1) = 0$$ $$\alpha = \frac{1}{3}, \frac{2}{3}, 3, \frac{1}{2}$$ $$x = 9, 4, \frac{4}{9}, 1$$ So, no. of solutions = 4

Question 10

Maths · Differential Equations · Single correct

Let $y = y(x)$ be the solution of the differential equation $\cos x \left( \log_e (\cos x) \right)^2 \, \mathrm{d}y + \left( \sin x - 3y \sin x \log_e (\cos x) \right) \, \mathrm{d}x = 0, x \in \left( 0, \frac{\pi}{2} \right)$. If $y \left( \frac{\pi}{4} \right) = \frac{-1}{\log_e 2}$, then $y \left( \frac{\pi}{6} \right)$ is equal to:

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

Answer: (a)

Solution

$\dfrac{dy}{dx}-\dfrac{3\sin x}{\cos x\,\ln\cos x}\,y=-\dfrac{\sin x}{\cos x\,(\ln\cos x)^2}$ I.F.$=e^{-\int\dfrac{3\tan x}{\ln\cos x}\,dx}$ Let $\ln\cos x=t$ $-\tan x\,dx=dt$ $I.F.=e^{3\int\dfrac{dt}{t}}=e^{3\ln t}=t^3=(\ln\cosx)^3$ $\therefore$ Solution will be$y(\ln\cos x)^3=-\int(\tan x)(\ln\cosx)\,dx$ $y(\ln\cos x)^3=-\dfrac{(\ln\cos x)^2}{2}+c$ $\because\;y\!\left(\dfrac{\pi}{4}\right)=\dfrac{1{\ln2}$ $\Rightarrow\;c=0$ $\therefore\;y=-\dfrac{1}{2(\ln\cos x)}$ $y\!\left(\dfrac{\pi}{6}\right)=-\dfrac12\times\dfrac{1}{\ln\!\left(\cos\dfrac{\pi}{6}\right)}$ $=-\dfrac12\times\dfrac{1}{\ln\!\left(\dfrac{\sqrt3}{2}\right)}$ $=-\dfrac12\times\dfrac{1}{\ln\sqrt3-\ln2}$ $=\dfrac{1}{\ln4-\ln3}$

Question 11

Maths · Sets · Single correct

Define a relation R on the interval $\left[0, \frac{\pi}{2}\right)$ by $xRy$ if and only if $\sec^2 x - \tan^2 y = 1$. Then R is :

  1. both reflexive and transitive but not symmetric
  2. an equivalence relation
  3. reflexive but neither symmetric not transitive
  4. both reflexive and symmetric but not transitive

Answer: (b)

Solution

Given $\sec^2 x - \tan^2 x = 1$ (on replacing $y$ with $x$). Reflexive: $$\sec^2 x - \tan^2 y = 1$$ $$1 + \tan^2 x + 1 - \sec^2 y = 1$$ $$\sec^2 y - \tan^2 x = 1$$ Symmetric: $$\sec^2 x - \tan^2 y = 1$$ $$\sec^2 y - \tan^2 z = 1$$ Adding both: $$\sec^2 x - \tan^2 y + \sec^2 y - \tan^2 z = 1 + 1$$ $$\sec^2 x + 1 - \tan^2 z = 2$$ $$\sec^2 x - \tan^2 z = 1$$ Transitive: Hence equivalence relation.

Question 12

Maths · Conic Sections · Single correct

Let the ellipse $E_1:\frac{x^2}{a^2}+\frac{y^2}{b^2}=1,\ a>b$ and $E_2:\frac{x^2}{A^2}+\frac{y^2}{B^2}=1,\ A<B$ have same eccentricity $\frac{1}{\sqrt{3}}$. Let the product of their lengths of latus rectums be $\frac{32}{\sqrt{3}}$, and the distance between the foci of $E_1$ be $4$. If $E_1$ and $E_2$ meet at $A,B,C$ and $D$, then the area of the quadrilateral $ABCD$ equals:

  1. $\frac{12}{5} \sqrt{6}$
  2. $6 \sqrt{6}$
  3. $\frac{18}{5} \sqrt{6}$
  4. $\frac{24}{5} \sqrt{6}$

Answer: (d)

Solution

Given $2ae = 4$. Therefore, $a = 2\sqrt{3}$. Thus, $1 - \frac{b^2}{12} = \frac{1}{3} \Rightarrow b^2 = 8$. $$\frac{2b^2}{a} \times \frac{2A^2}{B} = \frac{32}{\sqrt{3}}$$ Therefore, $$\frac{2 \times 8}{2\sqrt{3}} \times \frac{2A^2}{B} = \frac{32}{\sqrt{3}}$$ This implies $$\frac{A^2}{B} = 2 \Rightarrow A^2 = 2B$$ $$1 - \frac{A^2}{B} = \frac{1}{3}$$ Therefore, $$B = 3 \Rightarrow A^2 = 6$$ Equation 1: $\frac{x^2}{12} + \frac{y^2}{5} = 1 \ldots (i)$ Equation 2: $\frac{x^2}{6} + \frac{y^2}{9} = 1 \ldots (ii)$ On solving (i) and (ii), $$(x, y) = \left( \frac{\sqrt{6}}{\sqrt{5}}, \frac{6}{\sqrt{5}} \right), \left( \frac{-\sqrt{6}}{\sqrt{5}}, \frac{6}{\sqrt{5}} \right), \left( \frac{\sqrt{6}}{\sqrt{5}}, \frac{-6}{\sqrt{5}} \right), \left( \frac{-\sqrt{6}}{\sqrt{5}}, \frac{-6}{\sqrt{5}} \right)$$ Four points are vertices of rectangle area $= \frac{24\sqrt{6}}{5}$.

Question 13

Maths · Sequences and Series · Single correct

Consider an A. P. of positive integers, whose sum of the first three terms is 54 and the sum of the first twenty terms lies between 1600 and 1800. Then its 11^{th} term is:

  1. 90
  2. 84
  3. 122
  4. 108

Answer: (a)

Solution

Given $S_3 = 3a + 3d = 54$. This implies $a + d = 18$. $S_{20} = 10(2a + 19d)$ $$10(36 + 17d)$$ This implies $1600 < 10(36 + 17d) < 1800$. Therefore, $160 < 36 + 17d < 180$. This simplifies to $124 < 17d < 144$. Dividing throughout by 17 gives $\frac{7}{17} < d < \frac{8}{17}$. The common difference will be a natural number. Thus, $d = 8$ implies $a = 10$. Finally, $a_{11} = 10 + 10 \times 8 = 90$.

Question 14

Maths · Three Dimensional Geometry · Single correct

Let $\mathbf{a} = \hat{i} + 2\hat{j} + \hat{k}$ and $\mathbf{b} = 2\hat{i} + 7\hat{j} + 3\hat{k}$. Let $\mathbf{L}_1 : \mathbf{r} = (-\hat{i} + 2\hat{j} + \hat{k}) + \lambda \mathbf{a}, \lambda \in \mathbb{R}$ and $\mathbf{L}_2 : \mathbf{r} = (\hat{j} + \hat{k}) + \mu \mathbf{b}, \mu \in \mathbb{R}$ be two lines. If the line $\mathbf{L}_3$ passes through the point of intersection of $\mathbf{L}_1$ and $\mathbf{L}_2$, and is parallel to $\mathbf{a} + \mathbf{b}$, then $\mathbf{L}_3$ passes through the point:

  1. (5, 17, 4)
  2. (2, 8, 5)
  3. (8, 26, 12)
  4. (-1, -1, 1)
Solution

Given $L_1: \vec{r} = (-\hat{i} + 2\hat{j} + \hat{k}) + \lambda (\hat{i} + 2\hat{j} + \hat{k})$. $$\Rightarrow \vec{r} = (\lambda - 1)\hat{i} + 2(\lambda + 1)\hat{j} + (\lambda + 1)\hat{k}$$ $L_2: \vec{r} = (\hat{j} + \hat{k}) + \mu (2\hat{i} + 7\hat{j} + 3\hat{k})$. $$\Rightarrow \vec{r} = 2\mu \hat{i} + (1 + 7\mu) \hat{j} + (1 + 3\mu) \hat{k}$$ For point of intersection equating respective components $$\Rightarrow \lambda - 1 = 2\mu$$ $$2(\lambda + 1) = 1 + 7\mu$$ $$\lambda + 1 = 1 + 3\mu$$ We get $$\Rightarrow \lambda = 3 and \mu = 1$$ $$\Rightarrow \vec{a} + \vec{b} = 3\hat{i} + 9\hat{j} + 4\hat{k}$$ $L_3: \vec{r} = 2\hat{i} + 8\hat{j} + 4\hat{k} + \alpha (3\hat{i} + 3\hat{j} + 4\hat{k})$. For $\alpha = 2$, $$\vec{r} = 8\hat{i} + 26\hat{j} + 12\hat{k}$$

Question 15

Maths · Sequences and Series · Single correct

The value of $\lim_{n \to \infty} \left( \sum_{k=1}^{n} \frac{k^3 + 6k^2 + 11k + 5}{(k+3)!} \right)$ is:

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

Answer: (d)

Solution

The given expression is $\($ $\lim$_{n $\to$ $\infty$} $\sum$_{k=1}^{n} $\frac{k^3 + 6k^2 + 11k + 5}{(k+3)!}$ $\)$. This can be rewritten as: $$ \lim_{n \to \infty} \sum_{k=1}^{n} \frac{k^3 + 6k^2 + 11k + 6 - 1}{(k+3)!} $$ Which simplifies to: $$ \lim_{n \to \infty} \sum_{k=1}^{n} \frac{(k+1)(k+2)(k+3) - 1}{(k+3)!} $$ Further simplification gives: $$ \lim_{n \to \infty} \sum_{k=1}^{n} \left( \frac{(k+1)(k+2)(k+3)}{(k+3)!} - \frac{1}{(k+3)!} \right) $$ This can be expressed as: $$ \lim_{n \to \infty} \sum_{k=1}^{n} \left( \frac{1}{k!} - \frac{1}{(k+3)!} \right) $$ Evaluating the series, we have: $$ \lim_{k=1} \left( \frac{1}{1!} + \frac{1}{2!} + \frac{1}{3!} + \frac{1}{4!} + \cdots + \frac{1}{n!} - \frac{1}{4!} - \frac{1}{5!} - \frac{1}{6!} - \cdots - \frac{1}{(n+3)!} \right) $$ This results in: $$ \frac{1}{1} + \frac{1}{2} + \frac{1}{6} = \frac{10}{6} = \frac{5}{3} $$

Question 16

Maths · Integrals · Single correct

The integral $80 \int_{0}^{\frac{\pi}{4}} \left( \frac{\sin \theta + \cos \theta}{9 + 16 \sin 2\theta} \right) d\theta$ is equal to:

  1. $3 \log_e 4$
  2. $4 \log_e 3$
  3. $6 \log_e 4$
  4. $2 \log_e 3$

Answer: (b)

Solution

Given $$I = \int_{0}^{\frac{\pi}{4}} \left( \frac{\sin \theta + \cos \theta}{9 - 16 \sin 2\theta} \right) d\theta$$ Take $\sin \theta - \cos \theta = t$. Then $(\cos \theta + \sin \theta) d\theta = dt$ and $(\sin \theta - \cos \theta)^2 = t^2$. Thus, $\sin 2\theta = 1 - t^2$. When $\theta = 0 \rightarrow t = -1$ and $\theta = \frac{\pi}{4} \rightarrow t = 0$. Therefore, $$I = \int_{-1}^{0} \frac{dt}{9 + 16(1 - t^2)}$$ $$= \frac{1}{16} \int_{-1}^{0} \frac{dt}{25 - 16t^2}$$ $$= \frac{1}{4} \left[ \frac{1}{10} \log \left| \frac{5 - 4t}{5 + 4t} \right| \right]_{-1}^{0}$$ $$= \frac{1}{40} [0 + \log_e 9]$$ Thus, $$I = \frac{\log_e 9}{40}$$ Therefore, $$80I = 2 \log_e 9$$ $$80I = 4 \log_e 3$$

Question 17

Maths · Three Dimensional Geometry · Single correct

Let $\mathbf{L}_1 : \frac{x-1}{1} = \frac{y-2}{-1} = \frac{z-1}{2}$ and $\mathbf{L}_2 : \frac{x+1}{-1} = \frac{y-2}{2} = \frac{z}{1}$ be two lines. Let $\mathbf{L}_3$ be a line passing through the point $(\alpha, \beta, \gamma)$ and be perpendicular to both $\mathbf{L}_1$ and $\mathbf{L}_2$. If $\mathbf{L}_3$ intersects $\mathbf{L}_1$, then $|5\alpha - 11\beta - 8\gamma|$ equals:

  1. 20
  2. 18
  3. 25
  4. 16

Answer: (c)

Solution

DR's of $L_3 = \vec{m} \times \vec{n} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ -1 & 2 & 2 \\ 2 & 1 & 1 \end{vmatrix}$ $$= -5\hat{i} - 3\hat{j} + \hat{k}$$ For $L_3$: $\($ $\frac{x - \alpha}{-5}$ = $\frac{y - \beta}{-3}$ = $\frac{z - \gamma}{1}$ = $\lambda$ $\)$ $A(\alpha - 5\lambda, \beta - 3\lambda, \gamma + \lambda)$ For $L_1$: $\($ $\frac{x - 1}{1}$ = $\frac{y - 2}{-1}$ = $\frac{z - 1}{2}$ = k $\)$ $B(k + 1, -k + 2, 2k + 1)$ Now $\alpha - 5\lambda = k + 1 \Rightarrow \alpha = 5\lambda + k + 1$ $\beta - 3\lambda = -k + 2 \Rightarrow \beta = 3\lambda - k + 2$ $\gamma + \lambda = 2k - 1 \Rightarrow \gamma = -\lambda + 2k - 1$ $|5\alpha - 11\beta - 8\gamma| = | - 25| = 25$

Question 18

Maths · Statistics · Single correct

Let $x_1, x_2, \ldots, x_{10}$ be ten observations such that $\sum_{i=1}^{10} (x_i - 2) = 30, \sum_{i=1}^{10} (x_i - \beta)^2 = 98, \beta > 2$, and their variance is $\frac{4}{5}$. If $\mu$ and $\sigma^2$ are respectively the mean and the variance of $2(x_1 - 1) + 4\beta, 2(x_2 - 1) + 4\beta, \ldots, 2(x_{10} - 1) + 4\beta$, then $\frac{\beta \mu}{\sigma^2}$ is equal to:

  1. 100
  2. 120
  3. 110
  4. 90

Answer: (a)

Solution

Given $\($ $\sum$_{l=1}^{10} (x_l - 2) = 30 $\)$ and $\($ $\sum$_{i=1}^{10} x_i = 50 $\)$. Therefore, Mean = 5. Variance = $\($ $\frac{4}{5}$ = $\frac{\sum x_l^2}{10}$ - ($\bar{x}$)^2 $\)$. $\[$ $\frac{4}{5}$ = $\frac{\sum x_l^2}{10}$ - 25 $\]$ $\[$ $\Rightarrow$ $\sum$ x_l^2 = 258 $\]$ Now, $\($ $\sum$_{l=1}^{10} (x_l - $\beta$)^2 = 98 $\)$ $\[$ $\sum$_{l=1}^{10} x_l^2 - 2$\beta$ $\sum$_{l=1}^{10} x_l + 10$\beta$^2 = 98 $\]$ $\[$ $\Rightarrow$ 258 - 2$\beta$(50) + 10$\beta$^2 = 98 $\]$ $\[$ $\Rightarrow$ 10$\beta$^2 - 100$\beta$ + 160 = 0 $\]$ $\[$ $\Rightarrow$ $\beta$^2 - 10$\beta$ + 16 = 0 $\]$ $\[$ $\Rightarrow$ $\beta$ = 8 as $\beta$ > 2 $\]$ Now, as per the question $\($ 2(x_1 - 1) + 4$\beta$, 2(x_2 - 1) + 4$\beta$, $\ldots$, 2(x_{10} - 1) + 4$\beta$ $\)$ Can be simplified as $\($ 2x_1 + 30, 2x_2 + 30, $\ldots$, 2x_{10} + 30 $\)$ $\($ $\mu$ = 2(5) + 30 = 40 $\)$ $\($ $\sigma$^2 = 2^2 $\left$( $\frac{4}{5}$ $\right$) = $\frac{16}{5}$ $\)$ $\($ $\beta$ $\mu$ = $\frac{8 \times 40}{\frac{16}{5}}$ = 100 $\)$

Question 19

Maths · Complex Numbers and Quadratic Equations · Single correct

Let $|z_1 - 8 - 2i| \leq 1$ and $|z_2 - 2 + 6i| \leq 2$, $z_1, z_2 \in \mathbb{C}$. Then the minimum value of $|z_1 - z_2|$ is:

  1. 13
  2. 10
  3. 3
  4. 7

Answer: (d)

Solution

Since $AB = \sqrt{100} = 10$, therefore $|Z_1 - Z_2|_{\min} = 10 - 2 - 1 = 7$.

Question 20

Maths · Determinants · Single correct

Let $\mathbf{A} = [a_{ij}] = \begin{bmatrix} \log_5 128 & \log_4 5 \\ \log_5 8 & \log_4 25 \end{bmatrix}$. If $A_{ij}$ is the cofactor of $a_{ij}$, $C_{ij} = \sum_{k=1}^{2} a_{ik} A_{jk}$, $1 \leq i,j \leq 2$, and $\mathbf{C} = [C_{ij}]$, then $8|\mathbf{C}|$ is equal to:

  1. 288
  2. 222
  3. 242
  4. 262

Answer: (c)

Solution

Given $|A| = \frac{11}{2}$. $$C_{11} = \sum_{k=1}^{2} a_{1k} \cdot A_{1k} = a_{11} A_{11} + a_{12} A_{12} = |A| = \frac{11}{2}$$ $$C_{12} = \sum_{k=1}^{2} a_{1k} \cdot A_{2k} = 0$$ $$C_{21} = \sum_{k=1}^{2} a_{2k} \cdot A_{1k} = 0$$ $$C_{22} = \sum_{k=1}^{2} a_{2k} \cdot A_{2k} = |A| = \frac{11}{2}$$ The matrix $C$ is given by: $$C = \begin{bmatrix} 11/2 & 0 \\ 0 & 11/2 \end{bmatrix}$$ The determinant $|C|$ is calculated as: $$|C| = \frac{121}{4}$$ Finally, $8|C|$ is: $$8|C| = 242$$

Question 21

Maths · Integrals · Numerical

Let $f : (0, \infty) \to \mathbb{R}$ be a twice differentiable function. If for some $a = 0$, $\int_{0}^{1} f(\lambda x) \, \mathrm{d}\lambda = a f(x)$, $f(1) = 1$ and $f(16) = \frac{1}{8}$, then $16 - f'\left(\frac{1}{16}\right)$ is equal to _____.

Answer: 112

Solution

Given, $\int_0^1 f(\lambda x) d\lambda = a f(x)$ Let $\lambda x = u$ $d\lambda = \frac{1}{x} du$ From (1) $\frac{1}{x} \int_0^x f(u) du = a f(x)$ $$\Rightarrow \int_0^x f(u) du = ax f(x)$$ Differentiate both sides $$f(x) = a (x f'(x) + f(x))$$ $$\Rightarrow f(x) = ax f'(x) + a f(x)$$ $$\Rightarrow (1 - a) f(x) = ax f'(x)$$ $$\Rightarrow f'(x) = \frac{(1 - a)}{a} \cdot \frac{1}{x} f(x)$$ Integrate both sides w.r.t. $(x)$ $$\Rightarrow \int \frac{f'(x)}{f(x)} dx = \frac{(1 - a)}{a} \int \frac{1}{x} dx$$ $$\Rightarrow \ln f(x) = \left( \frac{1 - a}{a} \right) \ln x + c$$ Now at $x = 1, f(1) = 1$ $$\Rightarrow c = 0$$ Also given $f(16) = \frac{1}{8}$ $$\Rightarrow 1 = (16)^{\frac{1-a}{a}}$$ $$\Rightarrow 8 = 2^{\frac{4-4a}{a}}$$ $$\Rightarrow 2^{-3} = 2^{\frac{4-4a}{a}}$$ $$\Rightarrow -3 = \frac{4-4a}{a}$$ $$\Rightarrow -3a = 4 - 4a$$ $$\Rightarrow a = 4$$ $$\therefore f(x) = x^{-3/4}$$ $$f(x) = \frac{-3}{4} x^{-7/4}$$ Put $x = \frac{1}{16}$ $$f'\left(\frac{1}{16}\right) = \frac{-3}{4} \left(\frac{1}{16}\right)^{-7/4} = \frac{-3}{4} \cdot 2^{-4x\left(\frac{-7}{4}\right)} = -96$$ $$\therefore 16 - f'\left(\frac{1}{16}\right) \Rightarrow 16 - (-96) = 112$$

Question 22

Maths · Matrices · Numerical

Let $S = \left\{ m \in \mathbb{Z} : A^{m^2} + A^m = 3I - A^{-6} \right\}$, where $A = \begin{bmatrix} 2 & -1 \\ 1 & 0 \end{bmatrix}$. Then $n(S)$ is equal to

Answer: 2

Solution

Given $A = \begin{bmatrix} 2 & -1 \\ 1 & 0 \end{bmatrix}$. Now finding characteristic equation $$\begin{vmatrix} 2 - \lambda & -1 \\ 1 & -\lambda \end{vmatrix} = 0$$ $$\Rightarrow (2 - \lambda)(-\lambda) - (-1)(1) = -2\lambda + \lambda^2 + 1 = 0$$ $$\Rightarrow \lambda^2 - 2\lambda + 1 = 0$$ $$\Rightarrow (\lambda - 1)^2 = 0$$ $$\Rightarrow \lambda = 1$$ Since $A$ satisfies $(A - I)^2 = 0$. Therefore, $A = I + N$ where $N = A - I$. $$N = \begin{bmatrix} 1 & -1 \\ 1 & -1 \end{bmatrix}$$ $$N^2 = 0$$ $$A^m = (I + N)^m = I + mN$$ $$A^m \cdot A^m = (I + mN)(I + mN) = I + 2mN + m^2N^2$$ Since $N^2 = 0$ $$\Rightarrow A^{m^2} = I + 2mN$$ Now putting in given condition $$I + m^2N + I + mN = 3I - A^{-6}$$ $$A^{-1} = \begin{bmatrix} 0 & 1 \\ -1 & 2 \end{bmatrix}$$ $$A^{-6} = (A^{-1})^6 = I + (-6)N$$ Therefore, putting in (i) $$(m^2 + m)N = I - (I - 6N)$$ $$(m^2 + m)N = 6N$$ Since $N \neq 0$ $$\Rightarrow m^2 + m = 6$$ $$\Rightarrow m^2 + m - 6 = 0$$ $$\Rightarrow (m - 2)(m + 3) = 0$$ $$\Rightarrow m = 2, -3$$ Number of elements in $S$ is 2.

Question 23

Maths · Limits and Derivatives · Numerical

Let [t] be the greatest integer less than or equal to t. Then the least value of p $\in$ $\mathbb{N}$ for which $$\lim_{x \to 0^+} \left( x \left( \left\lfloor \frac{1}{x} \right\rfloor + \left\lfloor \frac{2}{x} \right\rfloor + \ldots + \left\lfloor \frac{p}{x} \right\rfloor \right) - x^2 \left( \left\lfloor \frac{1}{x^2} \right\rfloor + \left\lfloor \frac{2^2}{x^2} \right\rfloor + \ldots + \left\lfloor \frac{9^2}{x^2} \right\rfloor \right) \right) \geq 1$$ is equal to _______.

Answer: 24

Solution

Given $$\lim_{x \to 0^+} \left( x \left( \left\lfloor \frac{1}{x} \right\rfloor + \left\lfloor \frac{2}{x} \right\rfloor + \ldots + \left\lfloor \frac{p}{x} \right\rfloor \right) - x^2 \left( \left\lfloor \frac{1^2}{x^2} \right\rfloor + \left\lfloor \frac{2^2}{x^2} \right\rfloor + \left\lfloor \frac{9^2}{x^2} \right\rfloor \right) \right) \geq 1$$ The expression $$\left( 1 + 2 + \ldots + p \right) - \left( 1^2 + 2^2 + \ldots + 9^2 \right) \geq 1$$ This simplifies to $$\frac{p(p+1)}{2} - \frac{9 \cdot 10 \cdot 19}{6} \geq 1$$ Thus, $$p(p+1) \geq 572$$ The least natural value of $$p$$ is 24.

Question 24

Maths · Permutations and Combinations · Fill in the blank

The number of 6-letter words, with or without meaning, that can be formed using the letters of the word MATHS such that any letter that appears in the word must appear at least twice, is

Answer: 1405

Solution

Q6. (i) Single letter is used, then number of words = 5 (ii) Two distinct letters are used, then number of words $$^5C_2 \times \left( \frac{6!}{2!4!} \times 2 + \frac{6!}{3!3!} \right) = 10(30 + 20) = 500$$ (iii) Three distinct letters are used, then number of words $$^5C_3 \times \frac{6!}{2!2!2!} = 900$$ Total number of words = 1405

Question 25

Maths · Inverse Trigonometric Functions · Numerical

Let $S = \left\{ x : \cos^{-1} x = \pi + \sin^{-1} x + \sin^{-1} (2x + 1) \right\}$. Then $\sum_{x \in S} (2x - 1)^2$ is equal to

Answer: 5

Solution

Given $\cos^{-1} x = \pi + \sin^{-1} x + \sin^{-1}(2x + 1)$. $2 \cos^{-1} x - \sin^{-1}(2x + 1) = \frac{3\pi}{2}$. Let $2\alpha - \beta = \frac{3\pi}{2}$ where $\cos^{-1} x = \alpha$, $\sin^{-1}(2x + 1) = \beta$. Then $2\alpha = \frac{3\pi}{2} + \beta$. We have $\cos 2\alpha = \sin \beta$. Thus, $2 \cos^2 \alpha - 1 = \sin \beta$. Substituting, $2x^2 - 1 = 2x + 1$. This simplifies to $x^2 - x - 1 = 0$. Solving, $\Rightarrow n = \frac{1 \pm \sqrt{5}}{2}$. Therefore, $$n = \begin{cases} \frac{1+\sqrt{5}}{2} & rejected \\ \frac{1-\sqrt{5}}{2} & \end{cases}$$ Thus, $4x^2 - 4x = 4$. Finally, $(2x - 1)^2 = 5$.

Physics

Question 26

Physics · Alternating Current · Single correct

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Choke coil is simply a coil having a large inductance but a small resistance. Choke coils are used with fluorescent mercury-tube fittings. If household electric power is directly connected to a mercury tube, the tube will be damaged. Reason (R): By using the choke coil, the voltage across the tube is reduced by a factor $\left( \frac{R}{R^2 + \omega^2 L^2} \right)$, where $\omega$ is frequency of the supply across resistor $R$ and inductor $L$. If the choke coil were not used, the voltage across the resistor would be the same as the applied voltage. In the light of the above statements, choose the most appropriate answer from the options given below:

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

Answer: (b)

Solution

The current $I$ in the circuit is given by the formula: $$I = \frac{V}{\sqrt{R^2 + \omega^2 L^2}}$$ The voltage across the resistor $V_R$ is given by: $$V_R = \frac{R}{\sqrt{R^2 + \omega^2 L^2}} V$$

Question 27

Physics · Motion in a Plane · Single correct

Two projectiles are fired with same initial speed from same point on ground at angles of $(45^\circ - \alpha)$ and $(45^\circ + \alpha)$, respectively, with the horizontal direction. The ratio of their maximum heights attained is:

  1. $\frac{1 - \tan \alpha}{1 + \tan \alpha}$
  2. $\frac{1 - \sin 2\alpha}{1 + \sin 2\alpha}$
  3. $\frac{1 + \sin 2\alpha}{1 - \sin 2\alpha}$
  4. $\frac{1 + \sin \alpha}{1 - \sin \alpha}$

Answer: (b)

Solution

The maximum height $H_{Max}$ is given by $$H_{Max} = \frac{(u \sin \theta)^2}{2g}$$ For $(H_{max})_1$, we have $u^2 \sin^2(45^\circ - \alpha)$. For $(H_{max})_2$, we have $u^2 \sin^2(45^\circ + \alpha)$. This can be expressed as $$\left( \frac{1}{\sqrt{2}} \cos \alpha - \frac{1}{\sqrt{2}} \sin \alpha \right)^2$$ which simplifies to $$\left( \frac{1}{\sqrt{2}} \cos \alpha + \frac{1}{\sqrt{2}} \sin \alpha \right)^2$$ Finally, this results in $$\frac{1 - \sin 2\alpha}{1 + \sin 2\alpha}$$

Question 28

Physics · Electric Charges and Fields · Single correct

An electric dipole of mass $m$, charge $q$, and length $l$ is placed in a uniform electric field $\mathbf{E} = E_0 \hat{i}$. When the dipole is rotated slightly from its equilibrium position and released, the time period of its oscillations will be:

  1. $\frac{1}{2\pi} \sqrt{\frac{ml}{2qE_0}}$
  2. $2\pi \sqrt{\frac{ml}{qE_0}}$
  3. $\frac{1}{2\pi} \sqrt{\frac{2ml}{qE_0}}$
  4. $2\pi \sqrt{\frac{ml}{2qE_0}}$

Answer: (d)

Solution

Given $\tau = PE_0 \sin \theta$. If $\theta$ is small, $\tau = -(PE_0) \theta$. $$I = m \left( \frac{l}{2} \right)^2 \cdot 2 = \frac{ml^2}{2}$$ $$T = 2\pi \sqrt{\frac{ml^2}{2 \cdot PE_0}} = 2\pi \sqrt{\frac{ml^2}{2 \cdot q/E_0}}$$ $$T = 2\pi \sqrt{\frac{ml}{2qE_0}}$$

Question 29

Physics · Physical World, Units and Measurements · Single correct

The pair of physical quantities not having same dimensions is:

  1. Pressure and Young's modulus
  2. Surface tension and impulse
  3. Torque and energy
  4. Angular momentum and Planck's constant

Answer: (b)

Solution

Q5. The dimension of angular momentum is $ML^2 T^{-1}$. The dimension of Planck's Constant is $ML^2 T^{-1}$. The dimension of torque is $ML^2 T^{-2}$. The dimension of energy is $ML^2 T^{-2}$. The dimension of surface tension is $MT^{-2}$. The dimension of impulse is $MLT^{-1}$. The dimension of pressure is $ML^{-1} T^{-2}$. The dimension of Young's modulus is $ML^{-1} T^{-2}$.

Question 30

Physics · Oscillations · Single correct

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Time period of a simple pendulum is longer at the top of a mountain than that at the base of the mountain. Reason (R): Time period of a simple pendulum decreases with increasing value of acceleration due to gravity and vice-versa. In the light of the above statements, choose the most appropriate answer from the options given below:

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

Answer: (a)

Solution

As $h$ increases, $g$ decreases, $T$ increases. $$T = 2\pi \sqrt{\frac{\ell}{g}}$$ $$g = \frac{g_0 R^2}{(R + h)^2}$$

Question 31

Physics · Physical World, Units and Measurements · Single correct

The expression given below shows the variation of velocity $(v)$ with time $(t)$, $v = At^2 + \frac{Bt}{C+t}$. The dimension of $ABC$ is:

  1. $[M^0 L^1 T^{-3}]$
  2. $[M^0 L^2 T^{-2}]$
  3. $[M^0 L^1 T^{-2}]$
  4. $[M^0 L^2 T^{-3}]$

Answer: (d)

Solution

Given $[LT^{-1}] = [A][T^2] = \frac{[B][T]}{[C] + [T]}$. We have $[C] = [T]$, $[A] = [LT^{-3}]$, $[B] = [LT^{-1}]$, and $[ABC] = [L^2 T^{-3}]$.

Question 32

Physics · Electromagnetic Induction · Single correct

Consider $I_1$ and $I_2$ as the currents flowing simultaneously in two nearby coils $1$ and $2$, respectively. If $L_1$ is the self-inductance of coil $1$ and $M_{12}$ is the mutual inductance of coil $1$ with respect to coil $2$, then the induced emf in coil $1$ is:

  1. $\varepsilon_1 = -L_1 \frac{dI_2}{dt} - M_{12} \frac{dI_1}{dt}$
  2. $\varepsilon_1 = -L_1 \frac{dI_1}{dt} - M_{12} \frac{dI_2}{dt}$
  3. $\varepsilon_1 = -L_1 \frac{dI_1}{dt} - M_{12} \frac{dI_1}{dt}$
  4. $\varepsilon_1 = -L_1 \frac{dI_1}{dt} + M_{12} \frac{dI_2}{dt}$

Answer: (b)

Solution

Given $\phi_1 = L_1 I_1 + M_{12} I_2$. The expression for $\varepsilon_1$ is given by $$\varepsilon_1 = -\frac{d\phi_1}{dt} = -L_1 \frac{dI_1}{dt} - M_{12} \frac{dI_2}{dt}.$$

Question 33

Physics · Ray Optics and Optical Instruments · Single correct

At the interface between two materials having refractive indices $n_1$ and $n_2$, the critical angle for reflection of an em wave is $\theta_{1C}$. The $n_2$ material is replaced by another material having refractive index $n_3$ such that the critical angle at the interface between $n_1$ and $n_3$ materials is $\theta_{2C}$. If $n_3 > n_2 > n_1$; $\frac{n_2}{n_3} = \frac{2}{5}$ and $\sin \theta_{2C} - \sin \theta_{1C} = \frac{1}{2}$, then $\theta_{1C}$ is

  1. $\sin^{-1} \left( \frac{1}{6} \right)$
  2. $\sin^{-1} \left( \frac{1}{3} \right)$
  3. $\sin^{-1} \left( -\frac{5}{6} \right)$
  4. $\sin^{-1} \left( \frac{2}{3} \right)$

Answer: (c)

Solution

Given $\sin \theta_{1C} = \frac{n_1}{n_2}$ and $\sin \theta_{2C} = \frac{n_1}{n_3}$. Then, $$\sin \theta_{2C} - \sin \theta_{1C} = \frac{1}{2}$$ Substituting the values, $$\frac{n_1}{n_3} - \frac{n_1}{n_2} = \frac{1}{2}$$ Simplifying, $$\frac{n_1 n_2 - n_1 n_3}{n_3 n_2} = \frac{1}{2}$$ This gives, $$n_1 \left( \frac{2}{5} - 1 \right) = \frac{n_2}{2}$$ Solving further, $$\frac{n_1}{n_2} = -\frac{5}{6}$$ Thus, $$= \sin^{-1} \left( -\frac{5}{6} \right)$$

Question 34

Physics · Moving Charges and Magnetism · Single correct

Consider a long straight wire of a circular cross-section (radius a) carrying a steady current I. The current is uniformly distributed across this cross-section. The distances from the centre of the wire's cross-section at which the magnetic field [inside the wire, outside the wire] is half of the maximum possible magnetic field, any where due to the wire, will be

  1. [a/4, 3a/2]
  2. [a/4, 2a]
  3. [a/2, 2a]
  4. [a/2, 3a]

Answer: (c)

Solution

Maximum possible magnetic field is at the surface. $$B_{max} = \frac{\mu_0 I}{2 \pi a}$$ $$\frac{B_{max}}{2} = \frac{\mu_0 I}{4 \pi a}$$ It can be obtained inside as well as outside the wire. For inside, $$\frac{\mu_0 I}{4 \pi a} = \frac{\mu_0 I r}{2 \pi a^2}$$ $$\Rightarrow r = \frac{a}{2}$$ For outside, $$\frac{\mu_0 I}{4 \pi a} = \frac{\mu_0 I}{2 \pi r}$$ $$\Rightarrow r = 2a$$ Correct answer $\left[ \frac{a}{2}, 2a \right]$

Question 35

Physics · Work, Energy and Power · Single correct

As shown below, bob $A$ of a pendulum having massless string of length $'R'$ is released from $60^\circ$ to the vertical. It hits another bob $B$ of half the mass that is at rest on a frictionless table in the center. Assuming elastic collision, the magnitude of the velocity of bob $A$ after the collision will be (take $g$ as acceleration due to gravity)

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

Answer: (d)

Solution

Velocity of a just before hitting: $$u = \sqrt{2g \frac{R}{2}} = \sqrt{gR}$$ Just after collision, let velocity of A and B are $v_1$ and $v_2$ respectively. Therefore, by COM: $$mu = mv_1 + \frac{m}{2} v_2$$ $$2v_1 + v_2 = 2u \ldots (i)$$ $$e = 1 = \frac{v_2 - v_1}{u}$$ $$\Rightarrow v_2 - v_1 = u \ldots (ii)$$ From (i) -(ii) $$\Rightarrow 3v_1 = u \Rightarrow v_1 = \frac{u}{3} = \frac{1}{3} \sqrt{gR}$$

Question 36

Physics · Dual Nature of Radiation and Matter · Single correct

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason ($R$). Assertion (A): Emission of electrons in photoelectric effect can be suppressed by applying a sufficiently negative electron potential to the photoemissive substance. Reason ($R$): A negative electric potential, which stops the emission of electrons from the surface of a photoemissive substance, varies linearly with frequency of incident radiation. In the light of the above statements, choose the most appropriate answer from the options given below:

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

Answer: (d)

Solution

Negative potential will slow the electrons and if it is sufficient, it will make the photocurrent zero. $$eVs = hf - \phi_0$$

Question 37

Physics · Electromagnetic Induction · Single correct

A coil of area A and N turns is rotating with angular velocity $\omega$ in a uniform magnetic field $\vec{B}$ about an axis perpendicular to $\vec{B}$. Magnetic flux $\phi$ and induced emf $\varepsilon$ across it, at an instant when $\vec{B}$ is parallel to the plane of coil, are:

  1. $\varphi = AB, \varepsilon = 0$
  2. $\varphi = 0, \varepsilon = 0$
  3. $\varphi = 0, \varepsilon = NAB\omega$
  4. $\varphi = AB, \varepsilon = NAB\omega$

Answer: (c)

Solution

Given $\phi = BAN \cdot \cos(\omega t)$. The induced emf $\varepsilon$ is given by $$\varepsilon = -\frac{d\phi}{dt} = BA\omega N \cdot \sin(\omega t).$$ When $B$ is parallel to the plane, $\omega t = \frac{\pi}{2}$. Thus, $\phi = 0$, and $\varepsilon = BA\omega N$.

Question 38

Physics · Mechanical Properties of Fluids · Single correct

The fractional compression $\left( \frac{\Delta V}{V} \right)$ of water at the depth of 2.5 km below the sea level is ______ $\%$. Given, the Bulk modulus of water $= 2 \times 10^9 \, \mathrm{N \, m^{-2}}$, density of water $= 10^3 \, \mathrm{kg \, m^{-3}}$, acceleration due to gravity $= g = 10 \, \mathrm{m \, s^{-2}}$.

  1. 1.25
  2. 1.0
  3. 1.75
  4. 1.5

Answer: (a)

Solution

Given $$B = \frac{\rho g h}{\left( \frac{\Delta v}{v} \right)}$$ $$\frac{\Delta v}{v} \times 100 = \frac{\rho g h}{B} \times 100$$ $$\frac{1000 \times 10 \times 2.5 \times 10^3}{2 \times 10^9} \times 100\%$$ $$= 1.25\%$$

Question 39

Physics · Dual Nature of Radiation and Matter · Single correct

If $\lambda$ and $K$ are de Broglie wavelength and kinetic energy, respectively, of a particle with constant mass. The correct graphical representation for the particle will be

Answer: (b)

Solution

Given $$\lambda = \frac{h}{mv} = \frac{h}{\sqrt{2mK}}$$ $$\lambda^2 = \frac{h^2}{2m} \left( \frac{1}{k} \right)$$ $$Y = cx^2$$ Upward facing parabola passing through origin.

Question 40

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

For the circuit shown above, equivalent GATE is:

  1. OR gate
  2. NAND gate
  3. NOT gate
  4. AND gate

Answer: (a)

Solution

The truth table is given as follows: \begin{tabular}{|c|c|c|} \hline A & B & Y \\ \hline 0 & 0 & 0 \\ \hline 0 & 1 & 1 \\ \hline 1 & 0 & 1 \\ \hline 1 & 1 & 1 \\ \hline \end{tabular} This is the truth table for an OR Gate.

Question 41

Physics · System of Particles and Rotational Motion · Single correct

A body of mass 'm' connected to a massless and unstretchable string goes in verticle circle of radius 'R' under gravity g. The other end of the string is fixed at the center of circle. If velocity at top of circular path is $n \sqrt{gR}$, where, $n \geq 1$, then ratio of kinetic energy of the body at bottom to that at top of the circle is

  1. $\frac{n^2}{n^2 + 4}$
  2. $\frac{n^2 + 4}{n^2}$
  3. $\frac{n + 4}{n}$
  4. $\frac{n}{n + 4}$

Answer: (b)

Solution

Given $v = n \sqrt{gR}$. The initial velocity $v_0$ is given by $$v_0 = \sqrt{v^2 + 2g(2R)}$$ Substituting $v = n \sqrt{gR}$, we have $$v_0 = \sqrt{n^2 gR + 4gR}$$ Therefore, $$\frac{k_{bottom}}{k_{trog}} = \frac{v_0^2}{v^2} = \frac{n^2 + 4}{n^2}$$

Question 42

Physics · Ray Optics and Optical Instruments · Single correct

Let $u$ and $v$ be the distances of the object and the image from a lens of focal length $f$. The correct graphical representation of $u$ and $v$ for a convex lens when $|u| > f$ is

Answer: (c)

Solution

Given the equation $(u + f)(v - f) = f^2$. The graph shows the relationship between $u$ and $v$. The axes are labeled $u$ and $v$ respectively.

Question 43

Physics · Electric Charges and Fields · Single correct

Match List - I with List - II. \vspace{0.3cm} \[ \begin{array}{clcl} \textbf{List-I} & & \textbf{List-II} & \\ (A) & \text{Electric field inside (distance } r > 0 \text{ from center) of a uniformly charged spherical shell} & (I) & \dfrac{\sigma}{\varepsilon_0}\\ & \text{with surface charge density } \sigma \text{, and radius } R. & (II) & \dfrac{\sigma}{2\varepsilon_0}\\ (B) & \text{Electric field at distance } r > 0 \text{ from a uniformly charged infinite plane sheet} & (III) & 0\\ & \text{with surface charge density } \sigma. & (IV) & \dfrac{\sigma R^2}{\varepsilon_0 r^2}\\ (C) & \text{Electric field outside (distance } r > 0 \text{ from center) of a uniformly charged spherical shell} & & \\ & \text{with surface charge density } \sigma \text{, and radius } R. & & \\ (D) & \text{Electric field between 2 oppositely charged infinite plane parallel sheets with uniform} & & \\ & \text{surface charge density } \sigma. & & \end{array} \] \vspace{0.3cm} Choose the correct answer from the options given below:

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

Answer: (a)

Solution

Inside uniformly charged spherical shell, $E = 0$ Therefore, $A \rightarrow \mathrm{III}$ For uniformly charged infinite plate $$E = \frac{\sigma}{2\varepsilon_0}$$ Therefore, $B \rightarrow \mathrm{II}$ Outside of spherical shell $$E = \frac{Q}{4\pi\varepsilon_0 r_2} = \frac{\sigma R^2}{\varepsilon_0 r^2}$$ Therefore, $C \rightarrow \mathrm{IV}$ Between two plates $E = \frac{\sigma}{\varepsilon_0}$ Therefore, $D \rightarrow \mathrm{I}$

Question 44

Physics · Kinetic Theory · Single correct

The workdone in an adiabatic change in an ideal gas depends upon only:

  1. change in its temperature
  2. change in its volume
  3. change in its pressure
  4. change in its specific heat

Answer: (a)

Solution

Work done in adiabatic process is given by $$\frac{nR \Delta T}{1 - \gamma}$$. So, it depends upon change in temperature.

Question 45

Physics · Electromagnetic Waves · Single correct

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason ($R$). Assertion (A) : Electromagnetic waves carry energy but not momentum. Reason ($R$): Mass of a photon is zero. In the light of the above statements, choose the most appropriate answer from the options given below :

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

Answer: (c)

Solution

EM wave carry both energy and momentum. Rest mass of photon is zero.

Question 46

Physics · System of Particles and Rotational Motion · Numerical

The coordinates of a particle with respect to origin in a given reference frame is $(1, 1, 1)$ meters. If a force of $\vec{F} = \hat{i} - \hat{j} + \hat{k}$ acts on the particle, then the magnitude of torque (with respect to origin) in z-direction is

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

Answer: (b)

Solution

The torque $\vec{\tau}$ acting on the particle with respect to the origin can be calculated using the cross product of the position vector $\vec{r}$ and the force vector $\vec{F}$: $$\vec{\tau} = \vec{r} \times \vec{F}$$ Given the position vector $\vec{r} = (1, 1, 1) \, \mathrm{m}$ and the force vector $\vec{F} = \hat{i} - \hat{j} + \hat{k}$, we need to calculate the cross product: $$\vec{\tau} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 1 & 1 & 1 \\ 1 & -1 & 1 \end{vmatrix}$$ Calculating the determinant, we have: $$\vec{\tau} = \hat{i}(1 \cdot 1 - 1 \cdot (-1)) - \hat{j}(1 \cdot 1 - 1 \cdot 1) + \hat{k}(1 \cdot (-1) - 1 \cdot 1)$$ This simplifies to: $$\vec{\tau} = \hat{i}(1 + 1) - \hat{j}(1 - 1) + \hat{k}(-1 - 1)$$ $$\vec{\tau} = 2\hat{i} - 0\hat{j} - 2\hat{k}$$ The torque vector is $\vec{\tau} = 2\hat{i} - 2\hat{k}$. To find the magnitude of the torque in the $z$-direction, we look at the $\hat{k}$ component: $$\tau_z = -2$$ The magnitude of torque in the $z$-direction is: $$|\tau_z| = 2 \, \mathrm{Nm}$$ Thus, the magnitude of the torque in the $z$-direction is 2 Newton-meters.

Question 47

Physics · Kinetic Theory · Fill in the blank

A container of fixed volume contains a gas at $27^\circ \mathrm{C}$. To double the pressure of the gas, the temperature of gas should be raised to _____$^\circ \mathrm{C}$.

Answer: 327

Solution

Given $V = constant$, we have the relation $$\frac{P_1}{T_1} = \frac{P_2}{T_2}.$$ Given $P_2 = 2P_1$ and $T_2 = 2T_1$, we find $$T_2 = 2 \times 300 = 600 \, K.$$ Therefore, $T_2 = 327^\circ C$.

Question 48

Physics · Ray Optics and Optical Instruments · Numerical

Two light beams fall on a transparent material block at point 1 and 2 with angle $\theta_1$ and $\theta_2$, respectively, as shown in figure. After refraction, the beams intersect at point 3 which is exactly on the interface at other end of the block. Given: the distance between 1 and 2, $d=4\sqrt{3}\,\mathrm{cm}$ and $\theta_1=\theta_2=\cos^{-1}\left(\frac{n_2}{2n_1}\right)$, where refractive index of the block $n_2>$ refractive index of the outside medium $n_1$, then the thickness of the block is $\underline{\hspace{2cm}}$ cm.

Answer: 6

Solution

Given $n_1 \sin(90^\circ - \theta_1) = n_2 \sin r$. $$n_1 \times \frac{n_2}{2n_1} = n_2 \sin r$$ $$\sin r = \frac{1}{2}$$ $$r = 30^\circ$$ $$\tan r = \left(\frac{d/2}{t}\right)$$ $$t = \frac{d}{2 \tan r} = \frac{d \sqrt{3}}{2} = \frac{(4 \sqrt{3}) \sqrt{3}}{2}$$ $$= 6 \, \mathrm{cm}$$

Question 49

Physics · Mechanical Properties of Fluids · Numerical

In a hydraulic lift, the surface area of the input piston is $6 \, \mathrm{cm}^2$ and that of the output piston is $1500 \, \mathrm{cm}^2$. If $100 \, \mathrm{N}$ force is applied to the input piston to raise the output piston by $20 \, \mathrm{cm}$, then the work done is ______ kJ.

Answer: 5

Solution

Given $F = 100 \, \mathrm{N}$, $A_1 = 6 \, \mathrm{cm^2}$, and $A_2 = 1500 \, \mathrm{cm^2}$. Using the formula $\frac{F_1}{A_1} = \frac{F_2}{A_2}$, we have: $$\frac{100}{6} = \frac{F}{1500}$$ Solving for $F$ gives: $$F = \frac{50}{3} \times 1500$$ Calculating $F$: $$F = 50 \times 500 = 25 \times 10^3 \, \mathrm{N}$$ The work done $\omega$ is given by $\vec{F} \cdot \vec{S}$: $$\omega = 25 \times 10^3 \times \frac{20}{100}$$ Simplifying gives: $$= 5 \times 10^3 = 5 \, \mathrm{kJ}$$

Question 50

Physics · Motion in a Plane · Numerical

The maximum speed of a boat in still water is $27 \, \mathrm{km/h}$. Now this boat is moving downstream in a river flowing at $9 \, \mathrm{km/h}$. A man in the boat throws a ball vertically upwards with speed of $10 \, \mathrm{m/s}$. Range of the ball as observed by an observer at rest on the river bank, is ______ cm. (Take $g = 10 \, \mathrm{m/s^2}$)

Answer: 2000

Solution

Given $\vec{v}_b = 9 + 27 = 36 \, \mathrm{km/hr}$. $$\vec{v}_b = 36 \times \frac{1000}{3600} = 10 \, \mathrm{m/sec}$$ Time of flight $= \frac{2 \times 10}{10} = 2 \, \mathrm{sec}$ Range $= 10 \times 2 = 20 \, \mathrm{m} = 2000 \, \mathrm{cm}$

Chemistry

Question 51

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

Total number of nucleophiles from the following is: $\mathrm{NH_3}$, $\mathrm{PhSH}$, $\mathrm{(H_3C)_2S}$, $\mathrm{H_2C=CH_2}$, $\overset{\ominus}{\mathrm{O}}\mathrm{H}$, $\mathrm{H_3O^\oplus}$, $\mathrm{(CH_3)_2CO}$, $\mathrm{>=NCH_3}$

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

Answer: (d)

Solution

Total five nucleophiles are present: $\mathrm{NH_3}$, $\mathrm{PhSH}$, $(\mathrm{H_3C})_2\mathrm{S}$, $\mathrm{CH_2} = \mathrm{CH_2}$, $\overset{\ominus}{\mathrm{O}}\mathrm{H}$.

Question 52

Chemistry · Electrochemistry · Single correct

The standard reduction potential values of some of the p-block ions are given below. Predict the one with the strongest oxidising capacity.

  1. $\mathrm{E}^{\Theta}_{\mathrm{Pb}^{4+}/\mathrm{Pb}^{2+}} = +1.67 \, \mathrm{V}$
  2. $\mathrm{E}^{\Theta}_{\mathrm{Sn}^{4+}/\mathrm{Sn}^{2+}} = +1.15 \, \mathrm{V}$
  3. $\mathrm{E}^{\Theta}_{\mathrm{Al}^{3+}/\mathrm{Al}} = -1.66 \, \mathrm{V}$
  4. $\mathrm{E}^{\circ}_{\mathrm{Tl}^{3+}/\mathrm{Tl}} = +1.26 \, \mathrm{V}$

Answer: (a)

Solution

The element having strongest oxidising capacity will have highest value of standard reduction potential.

Question 53

Chemistry · Electrochemistry · Single correct

The molar conductivity of a weak electrolyte when plotted against the square root of its concentration, which of the following is expected to be observed?

  1. A small decrease in molar conductivity is observed at infinite dilution.
  2. Molar conductivity decreases sharply with increase in concentration.
  3. A small increase in molar conductivity is observed at infinite dilution.
  4. Molar conductivity increases sharply with increase in concentration.

Answer: (b)

Solution

For a weak electrolyte, the variation of $\Lambda_m$ with $\sqrt{c}$ is shown in the graph. The graph depicts a curve that decreases as $\sqrt{c}$ increases.

Question 54

Chemistry · Equilibrium · Single correct

At temperature T, compound $\mathrm{AB}_2{(g)}$ dissociates as $\mathrm{AB}_2{(g)} \rightleftharpoons \mathrm{AB}{(g)} + \frac{1}{2} \mathrm{B}_2{(g)}$ having degree of dissociation $x$ (small compared to unity). The correct expression for $x$ in terms of $K_p$ and $p$ is

  1. $\sqrt[4]{\frac{2K_p}{p}}$
  2. $\sqrt[3]{\frac{2K_p}{p}}$
  3. $\sqrt[3]{\frac{2K_p^2}{p}}$
  4. $\sqrt{\frac{K_p}{p}}$

Answer: (b)

Solution

For the reaction $\mathrm{AB_2(g) \rightleftharpoons AB(g) + \frac{1}{2} B_2(g)}$, at time $t = 0$, the initial pressure is $p_0$. At equilibrium, $t = t_{eq}$, the pressures are $p_0(1-x)$ for $\mathrm{AB_2}$, $p_0 x$ for $\mathrm{AB}$, and $\frac{p_0 x}{2}$ for $\mathrm{B_2}$. The total pressure $p$ is given by: $$p = p_0 x - p_0 x + p_0 x + \frac{p_0 x}{2}$$ Simplifying, we have: $$p = p_0 \left(1 + \frac{x}{2}\right)$$ Thus, $p_0$ is: $$p_0 = \frac{p}{\left(1 + \frac{x}{2}\right)}$$ The equilibrium constant $K_p$ is: $$K_p = \left( p_{AB} \right) \left( p_{B_2} \right)^{1/2}$$ Substituting the pressures, we get: $$K_p = \left( p_{0} x \right) \left( \frac{p_{0} x}{2} \right)^{1/2}$$ Simplifying further: $$K_p = \frac{p_0 (1-x)}{\left(1 + \frac{x}{2}\right)} \left( \frac{p}{1 + \frac{x}{2}} \times \frac{x}{2} \right)^{1/2}$$ Since $x \ll 1$, we approximate: $$K_p = p^{1/2} x^{3/2} \left(2\right)^{1/2}$$ Solving for $x$, we have: $$x = \sqrt[3]{\frac{2 K_p^2}{p}}$$

Question 55

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

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

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

Answer: (a)

Solution

The structure in option (A) is a linear chain with an ethyl group at the third carbon and a methyl group at the fifth carbon. This corresponds to the name 3-Ethyl-5-methylheptane. The structure in option (B) is a different configuration.

Question 56

Chemistry · Some Basic Concepts of Chemistry · Single correct

Choose the correct statements. (A) Weight of a substance is the amount of matter present in it. (B) Mass is the force exerted by gravity on an object. (C) Volume is the amount of space occupied by a substance. (D) Temperatures below $0^\circ \mathrm{C}$ are possible in Celsius scale, but in Kelvin scale negative temperature is not possible. (E) Precision refers to the closeness of various measurements for the same quantity. Choose the correct answer from the options given below:

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

Answer: (b)

Solution

Mass of substance is amount of matter present in it. Weight is force exerted by gravity on object.

Question 57

Chemistry · Co-ordination Compounds · Single correct

The correct increasing order of stability of the complexes based on $\Delta_o$ value is: I. $[\mathrm{Mn(CN)}_6]^{3-}$ II. $[\mathrm{Co(CN)}_6]^{4-}$ III. $[\mathrm{Fe(CN)}_6]^{4-}$ IV. $[\mathrm{Fe(CN)}_6]^{3-}$

  1. IV < III < II < I
  2. I < II < IV < III
  3. III < II < IV < I
  4. II < III < I < IV

Answer: (b)

Solution

Neglecting pairing energy I. $[\mathrm{Mn(CN)B}]^{3-} \Rightarrow \mathrm{Mn}^{3+}, \ t_2 \ g^4$, CFSE $= -0.4 \times 4 \Delta o = -1.6 \Delta$. II. $[\mathrm{Co(CN)8}]^{4-} \Rightarrow \mathrm{Co}^{2+}, \ t_2^6 e_g^1$, CFSE $= -0.4 \times 6 + 0.6 \times 1 = -1.8 \Delta$ III. $[\mathrm{Fe(CN)8}]^{4-} \Rightarrow \mathrm{Fe}^{2+}, \ t_{2g}^6 e_g^0$, CFSE $= -0.4 \times 6 = -2.4 \Delta_0$ IV. $[\mathrm{Fe(CN)8}]^{3-} \Rightarrow \mathrm{Fe}^{3+}, \ t_{2g}^5 e_g^0$, CFSE $= -0.4 \times 5 = -2 \Delta_0$ Order of stability III > IV > II > I

Question 58

Chemistry · Co-ordination Compounds · Single correct

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

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

Answer: (a)

Solution

For (A) $[\mathrm{MnBr_4}]^{2-}$, $\mathrm{Mn}^{+2} \Rightarrow [\mathrm{Ar}] 3d^5$. In presence of ligand field: $$\Rightarrow [\mathrm{Ar}] \uparrow \uparrow \uparrow \uparrow \uparrow \square \square \square$$ This leads to $sp^3$ hybridization, paramagnetic in nature. For (B) $[\mathrm{FeF_6}]^{3-}$, $\mathrm{Fe}^{+3} \Rightarrow [\mathrm{Ar}] 3d^5$. In presence of ligand field: $$\Rightarrow [\mathrm{Ar}] \uparrow \uparrow \uparrow \uparrow \uparrow \square \square \square \square \square \square$$ This leads to $sp^3d^2$ hybridization, paramagnetic in nature. For (C) $[\mathrm{Co(C_2O_4)_3}]^{3-}$, $\mathrm{Co}^{+3} \Rightarrow [\mathrm{Ar}] 3d^6$. In presence of ligand field: $$\Rightarrow [\mathrm{Ar}] \uparrow\downarrow \uparrow\downarrow \uparrow\downarrow \square \square \square$$ This leads to $d^2sp^3$ hybridization, diamagnetic in nature. For (D) $[\mathrm{Ni(CO)_4}]$, $\mathrm{Ni}^{0} \Rightarrow [\mathrm{Ar}] 3d^8 4s^2$. In presence of ligand field: $$\Rightarrow [\mathrm{Ar}] \uparrow\downarrow \uparrow\downarrow \uparrow\downarrow \uparrow\downarrow \uparrow\downarrow \square \square$$ This leads to $sp^3$ hybridization, diamagnetic in nature.

Question 59

Chemistry · Hydrocarbons · Single correct

In the following substitution reaction: product 'P' formed is:

Answer: (d)

Solution

Br at the para position of $\mathrm{NO_2}$ will undergo aromatic nucleophilic substitution by nucleophile $\mathrm{C_2H_5ONa}$.

Question 60

Chemistry · Electrochemistry · Single correct

For a Mg $\mid$ Mg$^{2+}$ (aq) $\mid$ Ag$^{+}$ (aq) $\mid$ Ag the correct Nernst Equation is:

  1. $E_{cell} = E^{\circ}_{cell} - \frac{RT}{2F} \ln \left( \frac{[Ag^{+}]}{[Mg^{2+}]} \right)$
  2. $E_{cell} = E^{\circ}_{cell} + \frac{RT}{2F} \ln \left( \frac{[Ag^{+}]^2}{[Mg^{2+}]} \right)$
  3. $E_{cell} = E^{\circ}_{cell} - \frac{RT}{2F} \ln \left( \frac{[Ag^{+}]^2}{[Mg^{2+}]} \right)$
  4. $E_{cell} = E^{\circ}_{cell} - \frac{RT}{2F} \ln \left( \frac{[Mg^{2+}]}{[Ag^{+}]} \right)$

Answer: (b)

Solution

Cathode: $\mathrm{Ag^+ (aq) + e^- \rightarrow Ag} \times 2$ Anode: $\mathrm{Mg \rightarrow Mg^{2+} (aq) + 2e^-}$ Cell reaction: $2\mathrm{Ag^+} + \mathrm{Mg} \rightarrow 2\mathrm{Ag} + \mathrm{Mg^{2+}}$ $Q = \frac{[\mathrm{Mg^{2+}}]}{[\mathrm{Ag^+}]^2}$ By Nernst equation $$E_{cell} = E^\circ_{cell} - \frac{RT}{nF} \ln Q$$ $$E_{cell} = E^\circ_{cell} - \frac{RT}{nF} \ln \left( \frac{[\mathrm{Mg^{2+}}]}{[\mathrm{Ag^+}]^2} \right)$$ $$= E^\circ_{cell} + \frac{RT}{2F} \ln \left( \frac{[\mathrm{Ag^+}]^2}{[\mathrm{Mg^{2+}}]} \right)$$

Question 61

Chemistry · Chemical Bonding and Molecular Structure · Single correct

The correct option with order of melting points of the pairs $(\mathrm{Mn, Fe})$, $(\mathrm{Tc, Ru})$ and $(\mathrm{Re, Os})$ is :

  1. $\mathrm{Fe}$ < $\mathrm{Mn}$, $\mathrm{Ru}$ < $\mathrm{Tc}$ and $\mathrm{Re}$ < $\mathrm{Os}$
  2. $\mathrm{Mn}$ < $\mathrm{Fe}$, $\mathrm{Tc}$ < $\mathrm{Ru}$ and $\mathrm{Os}$ < $\mathrm{Re}$
  3. $\mathrm{Mn}$ < $\mathrm{Fe}$, $\mathrm{Tc}$ < $\mathrm{Ru}$ and $\mathrm{Re}$ < $\mathrm{Os}$
  4. $\mathrm{Fe}$ < $\mathrm{Mn}$, $\mathrm{Ru}$ < $\mathrm{Tc}$ and $\mathrm{Os}$ < $\mathrm{Re}$

Answer: (b)

Solution

Melting point order: $\mathrm{Fe} > \mathrm{Mn}$, $\mathrm{Ru} > \mathrm{Tc}$, $\mathrm{Re} > \mathrm{Os}$.

Question 62

Chemistry · Solutions · Single correct

$1.24\,\mathrm{g}$ of $\mathrm{AX_2}$ (molar mass $124\,\mathrm{g\,mol^{-1}}$) is dissolved in $1\,\mathrm{kg}$ of water to form a solution with a boiling point of $100.0156^\circ\mathrm{C}$. Similarly, $25.4\,\mathrm{g}$ of $\mathrm{AY_2}$ (molar mass $250\,\mathrm{g\,mol^{-1}}$) dissolved in $2\,\mathrm{kg}$ of water constitutes a solution with a boiling point of $100.0260^\circ\mathrm{C}$. Given: $K_b(\mathrm{H_2O})=0.52\,\mathrm{K\,kg\,mol^{-1}}$.

  1. $\mathrm{AX_2}$ is fully ionised while $\mathrm{AY_2}$ is completely unionised.
  2. $\mathrm{AX_2}$ is completely unionised while $\mathrm{AY_2}$ is fully ionised.
  3. $\mathrm{AX_2}$ and $\mathrm{AY_2}$ (both) are completely unionised.
  4. $\mathrm{AX_2}$ and $\mathrm{AY_2}$ (both) are fully ionised

Answer: (a)

Solution

For $\mathrm{AX_2}$ $$\Delta T_b = i \, K \, m$$ $$0.0156 = i \times 0.52 \times \frac{1.24}{124 \times 1}$$ $$3 = i$$ $$3 = 1 + 2\alpha$$ $$1 = \alpha$$ For $\mathrm{AY_2}$ $$\Delta T_b = i \, K_b \, m$$ $$0.0260 = i \times 0.52 \times \frac{25.4}{250 \times 2}$$ $$i \approx 1$$ Therefore, $\mathrm{AX_2}$ is completely ionised and $\mathrm{AY_2}$ is completely unionised.

Question 63

Chemistry · Thermodynamics · Single correct

$500\,\mathrm{J}$ of energy is transferred as heat to $0.5\,\mathrm{mol}$ of Argon gas at $298\,\mathrm{K}$ and $1.00\,\mathrm{atm}$. The final temperature and the change in internal energy respectively are: Given: $R=8.3\,\mathrm{J\,K^{-1}\,mol^{-1}}$

  1. 378 \, \mathrm{K} and 500 \, \mathrm{J}
  2. 368 \, \mathrm{K} and 500 \, \mathrm{J}
  3. 348 \, \mathrm{K} and 300 \, \mathrm{J}
  4. 378 \, \mathrm{K} and 300 \, \mathrm{J}

Answer: (d)

Solution

Given $q_p = n \times c_p \times \Delta T$. $$500 = 0.5 \times \frac{5}{2} \times 8.3 \left( T_f - 298 \right)$$ Therefore, $T_f \approx 346.2 \, \mathrm{K}$. The ratio $\frac{\Delta H}{\Delta U} = \frac{C_p}{C_v} = \left( \frac{5}{3} \right)$. Thus, $\Delta U = \frac{3}{5} \times 500 = 300 \, \mathrm{J}$.

Question 64

Chemistry · Chemical Kinetics and Nuclear Chemistry · Single correct

The reaction $\mathrm{A_2+B_2\rightarrow2AB}$ follows the mechanism $$\mathrm{A_2\underset{k_{-1}}{\overset{k_1}{\rightleftharpoons}}A+A}\ \text{(fast)}$$ $$\mathrm{A+B_2\xrightarrow{k_2}AB+B}\ \text{(slow)}$$ $$\mathrm{A+B\rightarrow AB}\ \text{(fast)}$$ The overall order of the reaction is:

  1. 2
  2. 2.5
  3. 3
  4. 1.5

Answer: (d)

Solution

Given the rate equation $rate = k_2 [A] [B_2]$. $$\left( \frac{k_1}{k_{-1}} \right) = \left( \frac{[A]^2}{[A_2]} \right)$$ This implies $[A] = \sqrt{\frac{k_1}{k_{-1}}} \cdot \sqrt{[A_2]}$. Substituting in (1), we get $$Rate = k_2 \sqrt{\frac{k_1}{k_{-1}}} \cdot [A_2]^{\frac{1}{2}} \cdot [B_2]$$ Therefore, the order is $$\left( \frac{3}{2} \right) = 1.5$$

Question 65

Chemistry · Structure of Atom · Single correct

If $a_0$ is denoted as the Bohr radius of hydrogen atom, then what is the de-Broglie wavelength $(\lambda)$ of the electron present in the second orbit of hydrogen atom? [n : any integer]

  1. $\frac{8\pi a_0}{n}$
  2. $\frac{2a_0}{n\pi}$
  3. $\frac{4n}{\pi a_0}$
  4. $\frac{4\pi a_0}{n}$

Answer: (c)

Solution

Bohr radius of hydrogen atom $\rightarrow a_0$ According to Bohr, the equation used to calculate the angular momentum of an electron in a hydrogen atom is $$mvr = \frac{nh}{2\pi} \ldots (i)$$ $m \rightarrow$ mass of electron $v \rightarrow$ velocity of electron $r \rightarrow$ radius of the orbit $n \rightarrow$ orbit number in which electron is present. Given that the electron is present in the second orbit, $n = 2$. The radius of the second orbit $r_2 = a_0 \times 2^2 = 4a_0$. General formula for radius of $n^{th}$ orbit, $$r_n = a_0 \times n^2$$ From (1) $$mvr = n \frac{h}{2\pi}$$ $$2\pi r = n \frac{h}{mv}$$ $\frac{h}{mv} = \lambda$ (de Broglie relationship, $\lambda \rightarrow$ de Broglie Wavelength) So, $2\pi r = n\lambda$. For the electron in the second orbit, $2\pi r_2 = n\lambda$. Substitute for $r_2$ $$2\pi \times 4a_0 = n\lambda$$ $$8\pi a_0 = n\lambda$$ Therefore, $\lambda = \frac{8\pi a_0}{n}$.

Question 66

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

The product (P) formed in the following reaction is :

Answer: (a)

Solution

It is Clemmensen reduction, it will not reduce ester. Ester cannot be reduced by Clemmensen reduction.

Question 67

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

An element $E'$ has the ionisation enthalpy value of $374 \, \mathrm{kJ \, mol^{-1}}$. $E'$ reacts with elements $A, B, C$ and $D$ with electron gain enthalpy values of $-328, -349, -325$ and $-295 \, \mathrm{kJ \, mol^{-1}}$, respectively. The correct order of the products $\mathrm{EA, EB, EC}$ and $\mathrm{ED}$ in terms of ionic character is:

  1. $\mathrm{ED > EC > EB > EA}$
  2. $\mathrm{EA > EB > EC > ED}$
  3. $\mathrm{EB > EA > EC > ED}$
  4. $\mathrm{ED > EC > EA > EB}$

Answer: (c)

Solution

The element having high value of Electron gain enthalpy (magnitude) will form a compound having higher ionic character so order of ionic character $$EB > EA > EC > ED$$

Question 68

Chemistry · Co-ordination Compounds · Single correct

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

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

Answer: (d)

Solution

Amylose: It is a plant based starch it has $\alpha - C_1 - C_4$ glycosidic linkage. Cellulose: It has $\beta - C_1 - C_4$ glycosidic linkage. Glycogen: It has $\alpha - C_1 - C_4$ and glycosidic linkage (animal starch). Amylopectin: It is a plant based with $\alpha - C_1 - C_4$ and $C_1 - C_6$ glycosidic linkage.

Question 69

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

The steam volatile compounds among the following are:

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

Answer: (d)

Solution

Both compounds (A) and (B) are steam volatile due to intramolecular hydrogen bonding.

Question 70

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

Given below are two statements: **Statement (I):** The radii of isoelectronic species increases in the order: $\mathrm{Mg^{2+} F>Br>I}$ 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. Statement I is correct but Statement II is incorrect
  3. Both Statement I and Statement II are incorrect
  4. Both Statement I and Statement II are correct

Answer: (d)

Solution

Given $r \propto q^{-}$ (for isoelectronic species) and $\propto \frac{1}{q^{+}}$. Therefore, Statement I is correct. Magnitude of electron gain enthalpy: $\mathrm{Cl} > \mathrm{F} > \mathrm{Br} > \mathrm{I}$.

Question 71

Chemistry · Amines · Numerical

Given below are some nitrogen containing compounds Each of them is treated with HCl separately. 1.0 g of the most basic compound will consume _______ mg of HCl. (Given molar mass in $\mathrm{g/mol}^{-1}$ C : 12, H : 1, O : 16, Cl : 35.5)

Answer: 341

Solution

Benzyl Amine is most basic due to localised lone pair. Mole of benzyl Amine $\Rightarrow \frac{1}{107} = 0.00934$ mole 1 Mole of Benzyl amine consumed 1 mole of HCl So, Mole of HCl consumed $\rightarrow 0.00934$ mole Mass of HCl consumed $\rightarrow 0.00934 \times$ molar mass of HCl $$= 0.00934 \times 36.5$$ $$= 0.341 \, \mathrm{gm}$$ $$= 341 \, \mathrm{mg}$$

Question 72

Chemistry · The d-and f-Block Elements · Numerical

The molar mass of the water insoluble product formed from the fusion of chromite ore ($\mathrm{FeCr_2O_4}$) with $\mathrm{Na_2CO_3}$ in presence of $\mathrm{O_2}$ is $\mathrm{gmol^{-1}}$.

Answer: 160

Solution

The insoluble product will be $\mathrm{Fe_2O_3}$. The molar mass is calculated as follows: molar mass $= 56 \times 2 + 16 \times 3$ $$= 112 + 48$$ $$= 160$$

Question 73

Chemistry · Chemical Bonding and Molecular Structure · Numerical

The sum of sigma ($\sigma$) and pi ($\pi$) bonds in Hex-1,3-dien-5-yne is .

Answer: 15

Solution

Number of $\sigma$ bond $= 11$. Number of $\pi$ bond $= 4$. $$\sigma + \pi = 11 + 4 = 15$$

Question 74

Chemistry · Solutions · Numerical

If $\mathrm{A}_2 \mathrm{B}$ is $30\%$ ionised in an aqueous solution, then the value of van't Hoff factor (i) is ______ $\times 10^{-1}$.

Answer: 16

Solution

The reaction is given as $\mathrm{AB_2} \rightleftharpoons \mathrm{A^{2+}} + 2\mathrm{B^-}$. Initially, the concentrations are $1$, $0$, and $0$. At equilibrium, the concentrations are $1 - \alpha$, $\alpha$, and $2\alpha$. The expression for $i$ is: $$i = 1 + 2\alpha$$ Substituting $\alpha = 0.3$: $$i = 1 + 2 \times (0.3)$$ $$= 1.6$$ $$= 16 \times 10^{-1}$$

Question 75

Chemistry · Alcohols, Phenols and Ethers · Numerical

0.1 mole of compound ' S ' will weigh _______ g. (Given molar mass in g mol$^{-1}$ C : 12, H : 1, O : 16)

Answer: 13

Solution

0.1 mole of compound (S) weight in gm = 0.1 $\times$ molar mass of compound (S) = 0.1 $\times$ 130 = 13 gm