JEE Main 29 January 2024 Shift 2 question paper with solutions

JEE Main 29 January 2024 Shift 2: all 90 questions in paper order (Maths, Physics, Chemistry) with the answer key and worked solutions. Free to read; attempt it as a timed 3-hour mock test.

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Maths

Question 1

Maths · Matrices · Single correct

Let $A = \begin{bmatrix} 2 & 1 & 2 \\ 6 & 2 & 11 \\ 3 & 3 & 2 \end{bmatrix}$ and $P = \begin{bmatrix} 1 & 2 & 0 \\ 5 & 0 & 2 \\ 7 & 1 & 5 \end{bmatrix}$. The sum of the prime factors of $|P^{-1}AP - 2I|$ is equal to

  1. 26
  2. 27
  3. 66
  4. 23

Answer: (a)

Solution

Given $|P^{-1}AP - 2I| = |P^{-1}AP - 2P^{-1}P|$. This equals $|P^{-1}(A - 2I)P|$. Using the property of determinants, this becomes $|P^{-1}||A - 2I||P|$. Since $|P^{-1}| = 1/|P|$, it simplifies to $|A - 2I|$. Calculating the determinant: $$\begin{vmatrix} 0 & 1 & 2 \\ 6 & 0 & 11 \\ 3 & 3 & 0 \end{vmatrix} = 69$$ So, the prime factors of 69 are 3 and 23. Thus, the sum is 26.

Question 2

Maths · Permutations and Combinations · Single correct

Number of ways of arranging 8 identical books into 4 identical shelves where any number of shelves may remain empty is equal to

  1. 18
  2. 16
  3. 12
  4. 15

Answer: (d)

Solution

3 Shelf empty: $(8, 0, 0, 0) \rightarrow 1 way$ $(7, 1, 0, 0)$ $(6, 2, 0, 0)$ 2 shelf empty: $(5, 3, 0, 0)$ $(4, 4, 0, 0) \rightarrow 4 ways$ 1 shelf empty: $(6, 1, 1, 0)$ $(4, 2, 1, 0)$ $(1, 2, 3, 2)$ $(2, 2, 2, 2)$ 0 Shelf empty: $(3, 3, 2, 0)$ $(4, 2, 2, 0) \rightarrow 5 ways$ $(5, 1, 1, 1)$ $(3, 3, 1, 1)$ $(4, 2, 1, 1) \rightarrow 5 ways$ Total $= 15 ways$

Question 3

Maths · Three Dimensional Geometry · Single correct

Let P(3, 2, 3), Q(4, 6, 2) and R(7, 3, 2) be the vertices of $\triangle$ PQR. Then, the angle $\angle$ QPR is

  1. $\frac{\pi}{6}$
  2. $\cos^{-1}\left(\frac{7}{18}\right)$
  3. $\cos^{-1}\left(\frac{1}{18}\right)$
  4. $\frac{\pi}{3}$

Answer: (d)

Solution

Direction ratio of PR = (4, 1, -1). Direction ratio of PQ = (1, 4, -1). Now, $\($ $\cos$ $\theta$ = $\left$| $\frac{4 + 4 + 1}{\sqrt{18} \cdot \sqrt{18}}$ $\right$| $\)$. $\($ $\theta$ = $\frac{\pi}{3}$ $\)$.

Question 4

Maths · Statistics · Single correct

If the mean and variance of five observations are $\frac{24}{5}$ and $\frac{194}{25}$ respectively and the mean of first four observations is $\frac{7}{2}$, then the variance of the first four observations in equal to

  1. $\frac{4}{5}$
  2. $\frac{77}{12}$
  3. $\frac{5}{4}$
  4. $\frac{105}{4}$

Answer: (c)

Solution

Given $\bar{X} = \frac{24}{5}$; $\sigma^2 = \frac{194}{25}$. Let first four observations be $x_1, x_2, x_3, x_4$. Here, $$\frac{x_1 + x_2 + x_3 + x_4 + x_5}{5} = \frac{24}{5} \cdots$$ Also, $$\frac{x_1 + x_2 + x_3 + x_4}{4} = \frac{7}{2}$$ which implies $$x_1 + x_2 + x_3 + x_4 = 14.$$ Now from equation 1, $x_5 = 10$. Now, $\sigma^2 = \frac{194}{25}$. $$\frac{x_1^2 + x_2^2 + x_3^2 + x_4^2 + x_5^2}{5} - \frac{576}{25} = \frac{194}{25}$$ which implies $$x_1^2 + x_2^2 + x_3^2 + x_4^2 = 54.$$ Now, variance of first 4 observations $$Var = \frac{\sum_{i=1}^{4} x_i^2}{4} - \left(\frac{\sum_{i=1}^{4} x_i}{4}\right)^2$$ $$= \frac{54}{4} - \frac{49}{4} = \frac{5}{4}.$$

Question 5

Maths · Applications of Derivatives · Single correct

The function $f(x) = 2x + 3(x)^{\frac{2}{3}}, x \in \mathbb{R}$, has

  1. exactly one point of local minima and no point of local maxima
  2. exactly one point of local maxima and no point of local minima
  3. exactly one point of local maxima and exactly one point of local minima
  4. exactly two points of local maxima and exactly one point of local minima

Answer: (c)

Solution

Given $f(x) = 2x + 3(x)^{\frac{2}{3}}$. The derivative is $f'(x) = 2 + 2x^{-\frac{1}{3}}$. This can be rewritten as: $$= 2 \left( 1 + \frac{1}{x^{\frac{1}{3}}} \right)$$ $$= 2 \left( \frac{x^{\frac{1}{3}} + 1}{x^{\frac{1}{3}}} \right)$$ The sign chart shows: - Positive for $x 0$ So, maxima (M) at $x = -1$ and minima (m) at $x = 0$.

Question 6

Maths · Complex Numbers and Quadratic Equations · Single correct

Let $r$ and $\theta$ respectively be the modulus and amplitude of the complex number $z = 2 - i \left( 2 \tan \frac{5\pi}{8} \right)$, then $(r, \theta)$ is equal to

  1. $\left( 2 \sec \frac{3\pi}{8}, \frac{3\pi}{8} \right)$
  2. $\left( 2 \sec \frac{3\pi}{8}, \frac{5\pi}{8} \right)$
  3. $\left( 2 \sec \frac{5\pi}{8}, \frac{3\pi}{8} \right)$
  4. $\left( 2 \sec \frac{11\pi}{8}, \frac{11\pi}{8} \right)$

Answer: (a)

Solution

Given $z = 2 - i \left( 2 \tan \frac{5\pi}{8} \right) = x + iy$ (let). $r = \sqrt{x^2 + y^2}$ and $\theta = \tan^{-1} \frac{y}{x}$. $$r = \sqrt{(2)^2 + \left( 2 \tan \frac{5\pi}{8} \right)^2}$$ $$= \left| 2 \sec \frac{5\pi}{8} \right| = \left| 2 \sec \left( \pi - \frac{3\pi}{8} \right) \right|$$ $$= 2 \sec \frac{3\pi}{8}$$ and $\theta = \tan^{-1} \left( \frac{-2 \tan \frac{5\pi}{8}}{2} \right)$. $$= \tan^{-1} \left( \tan \left( \pi - \frac{5\pi}{8} \right) \right)$$ $$= \frac{3\pi}{8}$$

Question 7

Maths · Trigonometric Functions · Single correct

The sum of the solutions $x \in \mathbb{R}$ of the equation $$\frac{3 \cos 2x + \cos^3 2x}{\cos^6 x - \sin^6 x} = x^3 - x^2 + 6$$ is

  1. 0
  2. 1
  3. -1
  4. 3

Answer: (c)

Solution

Given $\($ $\frac{3 \cos 2x + \cos^3 2x}{\cos^6 x - \sin^6 x}$ = x^3 - x^2 + 6 $\)$. This implies $$ \frac{\cos 2x \left( 3 + \cos^2 2x \right)}{\cos 2x \left( 1 - \sin^2 x \cos^2 x \right)} = x^3 - x^2 + 6 $$ which simplifies to $$ \frac{4 \left( 3 + \cos^2 2x \right)}{\left( 4 - \sin^2 2x \right)} = x^3 - x^2 + 6 $$ Further simplifying gives $$ \frac{4 \left( 3 + \cos^2 2x \right)}{\left( 3 + \cos^2 2x \right)} = x^3 - x^2 + 6 $$ Thus, $$ x^3 - x^2 + 2 = 0 \Rightarrow (x + 1) \left( x^2 - 2x + 2 \right) = 0 $$ So, the sum of real solutions is $\($-1$\)$.

Question 8

Maths · Vector Algebra · Single correct

Let $\overrightarrow{OA} = \overrightarrow{a}$, $\overrightarrow{OB} = 12 \overrightarrow{a} + 4 \overrightarrow{b}$ and $\overrightarrow{OC} = \overrightarrow{b}$, where O is the origin. If S is the parallelogram with adjacent sides OA and OC, then $$ \frac{\text{area of the quadrilateral OABC}}{\text{area of S}} $$ is equal to

  1. 6
  2. 10
  3. 7
  4. 8

Answer: (d)

Solution

Area of parallelogram, $S = |\vec{a} \times \vec{b}|$. Area of quadrilateral = Area($\triangle OAB$) + Area($\triangle OBC$). $$= \frac{1}{2} \{ |\vec{a} \times (12 \vec{a} + 4 \vec{b})| + |\vec{b} \times (12 \vec{a} + 4 \vec{b})| \}$$ $$= 8 |(\vec{a} \times \vec{b})|$$ Ratio $= \frac{8 |(\vec{a} \times \vec{b})|}{|(\vec{a} \times \vec{b})|} = 8$

Question 9

Maths · Sequences and Series · Single correct

If $\log_e a$, $\log_e b$, $\log_e c$ are in an A.P. and $\log_e a - \log_e 2b$, $\log_e 2b - \log_e 3c$, $\log_e 3c - \log_e a$ are also in an A.P., then $a : b : c$ is equal to

  1. 9 : 6 : 4
  2. 16 : 4 : 1
  3. 25 : 10 : 4
  4. 6 : 3 : 2

Answer: (a)

Solution

Given $\log_e a$, $\log_e b$, $\log_e c$ are in A.P. Therefore, $b^2 = ac \ldots (i)$ Also $\log_e \left( \frac{a}{2b} \right)$, $\log_e \left( \frac{2b}{3c} \right)$, $\log_e \left( \frac{3c}{a} \right)$ are in A.P. $$\left( \frac{2b}{3c} \right)^2 = \frac{a}{2b} \times \frac{3c}{a}$$ $$\frac{b}{c} = \frac{3}{2}$$ Putting in eq. (i) $b^2 = a \times \frac{2b}{3}$ $$\frac{a}{b} = \frac{3}{2}$$ $a : b : c = 9 : 6 : 4$

Question 10

Maths · Integrals · Single correct

If $$\int \frac{\sin^{\frac{3}{2}} x + \cos^{\frac{3}{2}} x}{\sqrt{\sin^3 x \cos^3 x \sin(x - \theta)}} \, dx = A\sqrt{\cos\theta\tan x-\sin\theta} +B\sqrt{\cos\theta-\sin\theta\cot x} +C$$ where C is the integration constant, then AB is equal to

  1. 4 $\csc$(2$\theta$)
  2. 4 $\sec$ $\theta$
  3. 2 $\sec$ $\theta$
  4. 8 $\csc$(2$\theta$)

Answer: (d)

Solution

Given $$\int \frac{\sin^{\frac{3}{2}} x + \cos^{\frac{3}{2}} x}{\sqrt{\sin^3 x \cos^3 x \sin(x - \theta)}} \, dx$$ Let $$I = \int \frac{\sin^{\frac{3}{2}} x + \cos^{\frac{3}{2}} x}{\sqrt{\sin^3 x \cos^3 x (\sin x \cos \theta - \cos x \sin \theta)}} \, dx$$ This can be rewritten as: $$= \int \frac{\sin^{\frac{3}{2}} x}{\sin^{\frac{3}{2}} x \cos^2 x \sqrt{\tan x \cos \theta - \sin \theta}} \, dx + \int \frac{\cos^{\frac{3}{2}} x}{\sin^2 x \cos^{\frac{3}{2}} x \sqrt{\cos \theta - \cot x \sin \theta}} \, dx$$ Let $$I = I_1 + I_2$$ For $I_1$, let $\tan x \cos \theta - \sin \theta = t^2$ Then $$\sec^2 x \, dx = \frac{2t \, dt}{\cos \theta}$$ For $I_2$, let $\cos \theta - \cot x \sin \theta = z^2$ Then $$\csc^2 x \, dx = \frac{2z \, dz}{\sin \theta}$$ Thus, $$I = I_1 + I_2$$ This becomes: $$= \int \frac{2t \, dt}{\cos \theta} + \int \frac{2z \, dz}{\sin \theta}$$ Simplifying gives: $$= \frac{2t}{\cos \theta} + \frac{2z}{\sin \theta}$$ Finally, $$= 2 \sec \theta \sqrt{\tan x \cos \theta - \sin \theta} + 2 \csc \theta \sqrt{\cos \theta - \cot x \sin \theta}$$ Comparing, we have $$AB = 8 \csc 2\theta$$

Question 11

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

The distance of the point $(2, 3)$ from the line $2x - 3y + 28 = 0$, measured parallel to the line $\sqrt{3}x - y + 1 = 0$, is equal to

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

Answer: (d)

Solution

Writing P in terms of parametric coordinates $2 + r \cos \theta, 3 + r \sin \theta$ as $\tan \theta = \sqrt{3}$ $$P \left( 2 + \frac{r}{2}, 3 + \frac{\sqrt{3}r}{2} \right)$$ P must satisfy $2x - 3y + 28 = 0$ So, $2 \left( 2 + \frac{r}{2} \right) - 3 \left( 3 + \frac{\sqrt{3}r}{2} \right) + 28 = 0$ We find $r = 4 + 6\sqrt{3}$

Question 12

Maths · Differential Equations · Single correct

If $\sin\left(\frac{y}{x}\right) = \log_e \left|x\right| + \frac{\alpha}{2}$ is the solution of the differential equation $x \cos\left(\frac{y}{x}\right) \frac{dy}{dx} = y \cos\left(\frac{y}{x}\right) + x$ and $y(1) = \frac{\pi}{3}$, then $\alpha^2$ is equal to

  1. 3
  2. 12
  3. 4
  4. 9

Answer: (a)

Solution

Differential equation: $$x \cos \frac{y}{x} \frac{dy}{dx} = y \cos \frac{y}{x} + x$$ $$\cos \frac{y}{x} \left[ x \frac{dy}{dx} - y \right] = x$$ Divide both sides by $x^2$ $$\cos \frac{y}{x} \left( \frac{x \frac{dy}{dx} - y}{x^2} \right) = \frac{1}{x}$$ Let $\frac{y}{x} = t$ $$\cos t \left( \frac{dt}{dx} \right) = \frac{1}{x}$$ $$\cos t \, dt = \frac{1}{x} \, dx$$ Integrating both sides $$\sin t = \ln |x| + c$$ $$\sin \frac{y}{x} = \ln |x| + c$$ Using $y(1) = \frac{\pi}{3}$, we get $c = \frac{\sqrt{3}}{2}$ So, $\alpha = \sqrt{3} \Rightarrow \alpha^2 = 3$

Question 13

Maths · Sequences and Series · Single correct

If each term of a geometric progression $a_1, a_2, a_3, \ldots$ with $a_1 = \frac{1}{8}$ and $a_2 \neq a_1$, is the arithmetic mean of the next two terms and $S_n = a_1 + a_2 + \ldots + a_n$, then $S_{20} - S_{18}$ is equal to

  1. $2^{15}$
  2. $-2^{18}$
  3. $2^{18}$
  4. $-2^{15}$

Answer: (d)

Solution

Let $r$'th term of the GP be $ar^{n-1}$. Given, $$2a_r = a_{r+1} + a_{r+2}$$ $$2ar^{n-1} = ar^n + ar^{n+1}$$ $$\frac{2}{r} = 1 + r$$ $$r^2 + r - 2 = 0$$ Hence, we get $r = -2$ (as $r \neq 1$). So, $S_{20} - S_{18} = (\text{Sum up to 20 terms}) - (\text{Sum up to 18 terms}) = T_{19} + T_{20}$ $$T_{19} + T_{20} = ar^{18}(1+r)$$ Putting the values $a = \dfrac{1}{8}$ and $r = -2$: $$T_{19} + T_{20} = -2^{15}$$

Question 14

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

Let A be the point of intersection of the lines $3x + 2y = 14$, $5x - y = 6$ and B be the point of intersection of the lines $4x + 3y = 8$, $6x + y = 5$. The distance of the point $P(5, -2)$ from the line AB is

  1. $\frac{13}{2}$
  2. 8
  3. $\frac{5}{2}$
  4. 6

Answer: (d)

Solution

Solving lines $L_1(3x + 2y = 14)$ and $L_2(5x - y = 6)$ to get $A(2, 4)$ and solving lines $L_3(4x + 3y = 8)$ and $L_4(6x + y = 5)$ to get $B\left(\frac{1}{2}, 2\right)$. Finding Eqn. of $AB : 4x - 3y + 4 = 0$. Calculate distance $PM$ $$\Rightarrow \left| \frac{4(5) - 3(-2) + 4}{5} \right| = 6$$

Question 15

Maths · Inverse Trigonometric Functions · Single correct

Let $x = \frac{m}{n}$ (m, n are co-prime natural numbers) be a solution of the equation $\cos \left( 2 \sin^{-1} x \right) = \frac{1}{9}$ and let $\alpha, \beta (\alpha > \beta)$ be the roots of the equation $mx^2 - nx - m + n = 0$. Then the point $(\alpha, \beta)$ lies on the line

  1. 3x + 2y = 2
  2. 5x - 8y = -9
  3. 3x - 2y = -2
  4. 5x + 8y = 9

Answer: (d)

Solution

Assume $\sin^{-1} x = \theta$. $$\cos(2\theta) = \frac{1}{9}$$ $$\sin \theta = \pm \frac{2}{3}$$ As $m$ and $n$ are co-prime natural numbers, $$x = \frac{2}{3}$$ i.e. $m = 2$, $n = 3$. So, the quadratic equation becomes $2x^2 - 3x + 1 = 0$ whose roots are $\alpha = 1$, $\beta = \frac{1}{2} \left(1, \frac{1}{2}\right)$ lies on $$5x + 8y = 9$$

Question 16

Maths · Applications of Derivatives · Single correct

The function $f(x) = \frac{x}{x^2 - 6x - 16}$, $x \in \mathbb{R} - \{-2, 8\}$

  1. decreases in $(-2, 8)$ and increases in $(-\infty, -2) \cup (8, \infty)$
  2. decreases in $(-\infty, -2) \cup (-2, 8)$
  3. decreases in $(-\infty, -2)$ and increases in $(8, \infty)$
  4. increases in $(-\infty, -2) \cup (-2, 8) \cup (8, \infty)$

Answer: (b)

Solution

Given $$f(x) = \frac{x}{x^2 - 6x - 16}$$ Now, $$f'(x) = \frac{-(x^2 + 16)}{(x^2 - 6x - 16)^2}$$ $$f'(x) < 0$$ Thus $f(x)$ is decreasing in $(-\infty, -2) \cup (-2, 8) \cup (8, \infty)$

Question 17

Maths · Continuity and Differentiability · Single correct

Let $y = \log_e \left( \frac{1-x^2}{1+x^2} \right)$, $-1 < x < 1$. Then at $x = \frac{1}{2}$, the value of $225 \left( y' - y'' \right)$ is equal to

  1. 732
  2. 746
  3. 742
  4. 736

Answer: (d)

Solution

Given $$y = \log_e \left( \frac{1-x^2}{1+x^2} \right)$$ Differentiating, $$\frac{dy}{dx} = y' = \frac{-4x}{1-x^4}$$ Again, $$\frac{d^2y}{dx^2} = y'' = \frac{-4(1+3x^4)}{(1-x^4)^2}$$ Again $$y' - y'' = \frac{-4x}{1-x^4} + \frac{4(1+3x^4)}{(1-x^4)^2}$$ At $x = \frac{1}{2}$, $$y' - y'' = \frac{736}{225}$$ Thus $$225 \left( y' - y'' \right) = 225 \times \frac{736}{225} = 736$$

Question 18

Maths · Relations and Functions · Single correct

If R is the smallest equivalence relation on the set {$1, 2, 3, 4$\} such that $\{$(1,2), (1,3)$\} \subseteq$ R, then the number of elements in R is $\ldots$

  1. 10
  2. 12
  3. 8
  4. 15

Answer: (a)

Solution

Question 19

Maths · Probability · Single correct

An integer is chosen at random from the integers 1, 2, 3, $\ldots$, 50. The probability that the chosen integer is a multiple of atleast one of 4, 6 and 7 is

  1. $\frac{8}{25}$
  2. $\frac{21}{50}$
  3. $\frac{9}{50}$
  4. $\frac{14}{25}$

Answer: (b)

Solution

Given set = {1, 2, 3, $\ldots$, 50$\}$ P(A) = Probability that number is multiple of 4 $P(B)$ = Probability that number is multiple of 6 $P(C)$ = Probability that number is multiple of 7 Now, $$P(A) = \frac{12}{50}, \; P(B) = \frac{8}{50}, \; P(C) = \frac{7}{50}$$ again $$P(A \cap B) = \frac{4}{50}, \; P(B \cap C) = \frac{1}{50}, \; P(A \cap C) = \frac{1}{50}$$ $$P(A \cap B \cap C) = 0$$ Thus $$P(A \cup B \cup C) = \frac{12}{50} + \frac{8}{50} + \frac{7}{50} - \frac{4}{50} - \frac{1}{50} - \frac{1}{50} + 0$$ $$= \frac{21}{50}$$

Question 20

Maths · Vector Algebra · Single correct

Let a unit vector $\hat{u} = x \hat{i} + y \hat{j} + z \hat{k}$ make angles $\frac{\pi}{2}$, $\frac{\pi}{3}$ and $\frac{2\pi}{3}$ with the vectors $\frac{1}{\sqrt{2}} \hat{i} + \frac{1}{\sqrt{2}} \hat{k}$, $\frac{1}{\sqrt{2}} \hat{j} + \frac{1}{\sqrt{2}} \hat{k}$ and $\frac{1}{\sqrt{2}} \hat{i} + \frac{1}{\sqrt{2}} \hat{j}$ respectively. If $\vec{v} = \frac{1}{\sqrt{2}} \hat{i} + \frac{1}{\sqrt{2}} \hat{j} + \frac{1}{\sqrt{2}} \hat{k}$, then $|\hat{u} - \vec{v}|^2$ is equal to

  1. $\frac{11}{2}$
  2. $\frac{5}{2}$
  3. 9
  4. 7

Answer: (b)

Solution

Unit vector $\mathbf{\hat{u}} = x \mathbf{\hat{i}} + y \mathbf{\hat{j}} + z \mathbf{\hat{k}}$. $$\mathbf{P}_1 = \frac{1}{\sqrt{2}} \mathbf{\hat{i}} + \frac{1}{\sqrt{2}} \mathbf{\hat{k}}, \mathbf{P}_2 = \frac{1}{\sqrt{2}} \mathbf{\hat{j}} + \frac{1}{\sqrt{2}} \mathbf{\hat{k}}$$ $$\mathbf{P}_3 = \frac{1}{\sqrt{2}} \mathbf{\hat{i}} + \frac{1}{\sqrt{2}} \mathbf{\hat{j}}$$ Now angle between $\mathbf{\hat{u}}$ and $\mathbf{P}_1 = \frac{\pi}{2}$. $$\mathbf{\hat{u}} \cdot \mathbf{P}_1 = 0 \Rightarrow \frac{x}{\sqrt{2}} + \frac{z}{\sqrt{2}} = 0$$ $$\Rightarrow x + z = 0 \ldots (i)$$ Angle between $\mathbf{\hat{u}}$ and $\mathbf{P}_2 = \frac{\pi}{3}$. $$\mathbf{\hat{u}} \cdot \mathbf{P}_2 = |\mathbf{\hat{u}}| \cdot |\mathbf{P}_2| \cos \frac{\pi}{3}$$ $$\Rightarrow \frac{y}{\sqrt{2}} + \frac{z}{\sqrt{2}} = \frac{1}{2} \Rightarrow y + z = \frac{1}{\sqrt{2}} \ldots (ii)$$ Angle between $\mathbf{\hat{u}}$ and $\mathbf{P}_3 = \frac{2\pi}{3}$. $$\mathbf{\hat{u}} \cdot \mathbf{P}_3 = |\mathbf{\hat{u}}| \cdot |\mathbf{P}_3| \cos \frac{2\pi}{3}$$ $$\Rightarrow \frac{x}{\sqrt{2}} + \frac{4}{\sqrt{2}} = -\frac{1}{2} \Rightarrow x + y = \frac{-1}{\sqrt{2}} \ldots (iii)$$ From equation (i), (ii) and (iii) we get $$x = -\frac{1}{\sqrt{2}}, y = 0, z = \frac{1}{\sqrt{2}}$$ Thus $\mathbf{\hat{u}} - \mathbf{\hat{v}} = -\frac{1}{\sqrt{2}} \mathbf{\hat{i}} + \frac{1}{\sqrt{2}} \mathbf{\hat{k}} - \frac{1}{\sqrt{2}} \mathbf{\hat{i}} - \frac{1}{\sqrt{2}} \mathbf{\hat{j}} - \frac{1}{\sqrt{2}} \mathbf{\hat{k}}$ $$\mathbf{\hat{u}} - \mathbf{\hat{v}} = \frac{-2}{\sqrt{2}} \mathbf{\hat{i}} - \frac{1}{\sqrt{2}} \mathbf{\hat{j}}$$ $$\therefore |\mathbf{\hat{u}} - \mathbf{\hat{v}}|^2 = \left( \sqrt{\frac{4}{2} + \frac{1}{2}} \right)^2 = \frac{5}{2}$$

Question 21

Maths · Complex Numbers and Quadratic Equations · Numerical

Let $\alpha$, $\beta$ be the roots of the equation $x^2 - \sqrt{6}x + 3 = 0$ such that $\mathrm{Im}(\alpha) > \mathrm{Im}(\beta)$. Let $a, b$ be integers not divisible by 3 and $n$ be a natural number such that $\frac{\alpha^{99}}{\beta} + \alpha^{98} = 3^n (a + ib)$, $i = \sqrt{-1}$. Then $n + a + b$ is equal to ______.

Answer: 49

Solution

Given the equation $x^2 - \sqrt{6}x + 6 = 0$, we have roots $\alpha$ and $\beta$. The roots are given by $$x = \frac{\sqrt{6} \pm i \sqrt{6}}{2} = \frac{\sqrt{6}}{2} (1 \pm i).$$ Thus, $$\alpha = \sqrt{3} \left( e^{i \frac{\pi}{4}} \right), \beta = \sqrt{3} \left( e^{-i \frac{\pi}{4}} \right).$$ Therefore, $$\frac{\alpha^{99}}{\beta} + \alpha^{98} = \alpha^{98} \left( \frac{\alpha}{\beta} + 1 \right).$$ This simplifies to $$\frac{\alpha^{98}(\alpha + \beta)}{\beta} = 3^{49} \left( e^{i 99 \frac{\pi}{4}} \right) \times \sqrt{2}.$$ Thus, $$3^{49} (-1 + i) = 3^n (a + ib).$$ So, $n = 49$, $a = -1$, $b = 1$. Finally, $n + a + b = 49 - 1 + 1 = 49.$

Question 22

Maths · Determinants · Numerical

Let for any three distinct consecutive terms $a$, $b$, $c$ of an A.P., the lines $ax + by + c = 0$ be concurrent at the point $P$ and $Q(\alpha, \beta)$ be a point such that the system of equations $$x + y + z = 6,$$ $$2x + 5y + \alpha z = \beta$$ and $$x + 2y + 3z = 4,$$ has infinitely many solutions. Then $(PQ)^2$ is equal to

Answer: 113

Solution

Given $a, b, c$ are in A.P. Therefore, $2b = a + c \Rightarrow a - 2b + c = 0$. Thus, $ax + by + c$ passes through the fixed point $(1, -2)$. Therefore, $P = (1, -2)$. For infinite solution, $D = D1 = D2 = D3 = 0$. $$D : \begin{vmatrix} 1 & 1 & 1 \\ 2 & 5 & \alpha \\ 1 & 2 & 3 \end{vmatrix} = 0$$ This implies $\alpha = 8$. $$D_1 : \begin{vmatrix} 6 & 1 & 1 \\ \beta & 5 & \alpha \\ 4 & 2 & 3 \end{vmatrix} = 0 \Rightarrow \beta = 6$$ Therefore, $Q = (8, 6)$. Thus, $PQ^2 = 113$.

Question 23

Maths · Conic Sections · Numerical

Let P($\alpha$, $\beta$) be a point on the parabola $y^2 = 4x$. If P also lies on the chord of the parabola $x^2 = 8y$ whose mid point is $\left(1, \frac{5}{4}\right)$. Then $(\alpha - 28)(\beta - 8)$ is equal to .

Answer: 192

Solution

Parabola is $x^2 = 8y$. Chord with mid point $(x_1, y_1)$ is $T = S_1$. Therefore, $xx_1 - 4(y + y_1) = x_1^2 - 8y_1$. Thus, $(x_1, y_1) = \left(1, \frac{5}{4}\right)$. Therefore, $x - 4\left(y + \frac{5}{4}\right) = 1 - 8 \times \frac{5}{4} = -9$. Therefore, $x - 4y + 4 = 0 \ldots (i)$. $(\alpha, \beta)$ lies on (i) and also on $y^2 = 4x$. Therefore, $\alpha - 4\beta + 4 = 0 \ldots (ii)$ and $\beta^2 = 4\alpha \ldots (iii)$. Solving (ii) and (iii), $\beta^2 = 4(4\beta - 4) \Rightarrow \beta^2 - 16\beta + 16 = 0$. Therefore, $\beta = 8 \pm 4\sqrt{3}$ and $\alpha = 4\beta - 4 = 28 \pm 16\sqrt{3}$. Thus, $(\alpha, \beta) = (28 + 16\sqrt{3}, 8 + 4\sqrt{3})$ and $(28 - 16\sqrt{3}, 8 - 4\sqrt{3})$. Therefore, $(\alpha - 28)(\beta - 8) = (\pm 16\sqrt{3})(\pm 4\sqrt{3}) = 192$.

Question 24

Maths · Integrals · Numerical

If $\int_{\frac{\pi}{6}}^{\frac{\pi}{3}} \sqrt{1-\sin 2x}\,dx=\alpha+\beta\sqrt{2}+\gamma\sqrt{3}$, where $\alpha$, $\beta$ and $\gamma$ are rational numbers, then $3\alpha+4\beta-\gamma$ is equal to _______

Answer: 6

Solution

The integral from $\frac{\pi}{6}$ to $\frac{\pi}{3}$ of $\sqrt{1 - \sin 2x} \, dx$ is evaluated as follows: $$= \int_{\frac{\pi}{6}}^{\frac{\pi}{3}} \sin x - \cos x \, dx$$ This can be split into two integrals: $$= \int_{\frac{\pi}{6}}^{\frac{\pi}{4}} (\cos x - \sin x) \, dx + \int_{\frac{\pi}{4}}^{\frac{\pi}{3}} (\sin x - \cos x) \, dx$$ Evaluating these integrals gives: $$= -1 + 2\sqrt{2} - \sqrt{3}$$ This can be expressed as: $$= \alpha + \beta \sqrt{2} + \gamma \sqrt{3}$$ Where $\alpha = -1$, $\beta = 2$, $\gamma = -1$. Finally, we have: $$3\alpha + 4\beta - \gamma = 6$$

Question 25

Maths · Applications of Integrals · Numerical

Let the area of the region $\{(x, y) : 0 \leq x \leq 3, 0 \leq y \leq \min \{x^2 + 2, 2x + 2\}\}$ be $A$. Then $12A$ is equal to

Answer: 164

Solution

The area is given by the integral: $$A = \int_{0}^{2} (x^2 + 2) \, dx + \int_{2}^{3} (2x + 2) \, dx$$ Calculating the integrals, we find: $$A = \frac{41}{3}$$ Therefore, multiplying by 12 gives: $$12A = 41 \times 4 = 164$$

Question 26

Maths · Three Dimensional Geometry · Numerical

Let O be the origin, and M and N be the points on the lines $\frac{x-5}{4} = \frac{y-4}{1} = \frac{z-5}{3}$ and $\frac{x+8}{12} = \frac{y+2}{5} = \frac{z+11}{9}$ respectively such that MN is the shortest distance between the given lines. Then $\overrightarrow{OM} \cdot \overrightarrow{ON}$ is equal to .

Answer: 9

Solution

Given $$L_1 : \frac{x - 5}{4} = \frac{y - 4}{1} = \frac{z - 5}{3} = \lambda$$ $$drs(4, 1, 3) = \mathbf{b_1}$$ $$M(4\lambda + 5, \lambda + 4, 3\lambda + 5)$$ $$L_2 : \frac{x + 8}{12} = \frac{y + 2}{5} = \frac{z + 11}{9} = \mu$$ $$N(12\mu - 8, 5\mu - 2, 9\mu - 11)$$ $$\overrightarrow{MN} = (4\lambda - 12\mu + 13, \lambda - 5\mu + 6, 3\lambda - 9\mu + 16) \ldots (1)$$ Now $$\overrightarrow{b_1} \times \overrightarrow{b_2} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 4 & 1 & 3 \\ 12 & 5 & 9 \end{vmatrix} = -6\hat{i} + 8\hat{k} \ldots (2)$$ Equation (1) and (2) $$\therefore \frac{4\lambda - 12\mu + 13}{-6} = \frac{\lambda - 5\mu + 6}{0} = \frac{3\lambda - 9\mu + 16}{8}$$ I and II $$\lambda - 5\mu + 6 = 0 \ldots (3)$$ I and III $$\lambda - 3\mu + 4 = 0 \ldots (4)$$ Solve (3) and (4) we get $$\lambda = -1, \mu = 1$$ $$\therefore M(1, 3, 2)$$ $$N(4, 3, -2)$$ $$\therefore \overrightarrow{OM} \cdot \overrightarrow{ON} = 4 + 9 - 4 = 9$$

Question 27

Maths · Continuity and Differentiability · Numerical

Let $f(x) = \sqrt{\lim_{r \to x} \left\{ \frac{2r^2[(f(r))^2 - f(x)f(r)]}{r^2 - x^2} - r^3 e^{\frac{f(r)}{r}} \right\}}$ be differentiable in $(-\infty, 0) \cup (0, \infty)$ and $f(1) = 1$. Then the value of $a$, such that $f(a) = 0$, is equal to ______.

Answer: 2

Solution

Given $f(1) = 1$, $f(a) = 0$. $$f^2(x) = \lim_{r \to x} \left( \frac{2r^2 \left( f^2(r) - f(x)f(r) \right)}{r^2 - x^2} - r^3 e^{\frac{f(x)}{r}} \right)$$ $$= \lim_{r \to x} \left( \frac{2r^2 f(r)}{r + x} \frac{(f(r) - f(x))}{r - x} - r^3 e^{\frac{f(x)}{r}} \right)$$ $$f^2(x) = \frac{2x^2 f(x)}{2x} f'(x) - x^3 e^{\frac{f(x)}{x}}$$ $$y^2 = xy \frac{dy}{dx} - x^3 e^{\frac{y}{x}}$$ $$\frac{y}{x} \frac{dy}{dx} - \frac{x^2}{y} e^{\frac{y}{x}}$$ Put $y = vx$ then $\frac{dy}{dx} = v + x \frac{dv}{dx}$. $$v = v + x \frac{dv}{dx} - \frac{x}{v} e^v$$ $$\frac{dv}{dx} = \frac{e^v}{v} \Rightarrow e^{-v} v dv = dx$$ Integrating both sides: $$e^v (x + c) + 1 + v = 0$$ $f(1) = 1 \Rightarrow x = 1, y = 1$ $$\Rightarrow c = -1 - \frac{2}{e}$$ $$e^v \left( -1 - \frac{2}{e} + x \right) + 1 + v = 0$$ $$e^{\frac{y}{x}} \left( -1 - \frac{2}{e} + x \right) + 1 + \frac{y}{x} = 0$$ $x = a, y = 0 \Rightarrow a = \frac{2}{e}$ $$ae = 2$$

Question 28

Maths · Binomial Theorem · Numerical

Remainder when $64^{32^{32}}$ is divided by 9 is equal to .

Answer: 1

Solution

Let $32^{32} = t$. $$64^{32^{32}} = 64^t = 8^{2t} = (9 - 1)^{2t}$$ $$= 9k + 1$$ Hence remainder = 1.

Question 29

Maths · Sets · Numerical

Let the set $C = \left\{ (x, y) \mid x^2 - 2^y = 2023, x, y \in \mathbb{N} \right\}$. Then $\sum_{(x,y)\in C} (x + y)$ is equal to

Answer: 46

Solution

Given the equation $x^2 - 2^y = 2023$. Solving for $x$ and $y$, we find $x = 45$ and $y = 1$. Therefore, the sum $$\sum_{(x,y)=C} (x+y) = 46.$$

Question 30

Maths · Limits and Derivatives · Numerical

Let the slope of the line $45x + 5y + 3 = 0$ be $27r_1 + \frac{9r_2}{2}$ for some $r_1$, $r_2 \in \mathbb{R}$. Then $$\lim_{x \to 3} \left( \int_{3}^{x} \frac{8t^2}{\frac{3r_2x}{2} - r_2x^2 - r_1x^3 - 3x} \, dt \right)$$ is equal to

Answer: 12

Solution

According to the question, $$27r_1 + \frac{9r_2}{2} = -9$$ $$\lim_{x \to 3} \frac{\int_3^x 8t^2 \, dt}{\frac{3r_2 x}{2} - r_2 x^2 - r_1 x^3 - 3x}$$ $$= \lim_{x \to 3} \frac{8x^2}{\frac{3r_2}{2} - 2r_2 x - 3r_1 x^2 - 3} (using LH' Rule)$$ $$= \frac{72}{\frac{3r_2}{2} - 6r_2 - 27r_1 - 3}$$ $$= \frac{72}{-\frac{9r_2}{2} - 27r_1 - 3}$$ $$= \frac{72}{9 - 3} = 12$$

Physics

Question 31

Physics · Dual Nature of Radiation and Matter · Single correct

Two sources of light emit with a power of 200 $\mathrm{W}$. The ratio of number of photons of visible light emitted by each source having wavelengths 300 $\mathrm{nm}$ and 500 $\mathrm{nm}$ respectively, will be:

  1. 1 : 5
  2. 1 : 3
  3. 5 : 3
  4. 3 : 5

Answer: (d)

Solution

Given $\($ $\mathbf{n_1}$ $\times$ $\frac{hc}{\lambda_1}$ = 200 $\)$ and $\($ $\mathbf{n_2}$ $\times$ $\frac{hc}{\lambda_2}$ = 200 $\)$. Therefore, $\($ $\frac{\mathbf{n_1}}{\mathbf{n_2}}$ = $\frac{\lambda_1}{\lambda_2}$ = $\frac{300}{500}$ $\)$. Simplifying gives $\($ $\frac{\mathbf{n_1}}{\mathbf{n_2}}$ = $\frac{3}{5}$ $\)$.

Question 32

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

The truth table for this given circuit is :

  1. \begin{tabular}{|c|c|c|} \hline A & B & Y \\ \hline 0 & 0 & 1 \\ \hline 0 & 1 & 1 \\ \hline 1 & 0 & 1 \\ \hline 1 & 1 & 0 \\ \hline \end{tabular}
  2. \begin{tabular}{|c|c|c|} \hline A & B & Y \\ \hline 0 & 0 & 0 \\ \hline 0 & 1 & 1 \\ \hline 1 & 0 & 0 \\ \hline 1 & 1 & 1 \\ \hline \end{tabular}
  3. \begin{tabular}{|c|c|c|} \hline A & B & Y \\ \hline 0 & 0 & 0 \\ \hline 0 & 1 & 0 \\ \hline 1 & 0 & 0 \\ \hline 1 & 1 & 1 \\ \hline \end{tabular}
  4. \begin{tabular}{|c|c|c|} \hline A & B & Y \\ \hline 0 & 0 & 1 \\ \hline 0 & 1 & 0 \\ \hline 1 & 0 & 1 \\ \hline 1 & 1 & 0 \\ \hline \end{tabular}

Answer: (b)

Solution

The expression for the output is given by $$Y = A \cdot \overline{B} + \overline{A} \cdot B.$$ This can be rewritten as $$= (A + \overline{A}) \cdot B.$$ Since $A + \overline{A} = 1$, we have $$Y = 1 \cdot B.$$ Therefore, the final output is $$Y = B.$$

Question 33

Physics · Mathematics in Physics · Single correct

A physical quantity $Q$ is found to depend on quantities $a, b, c$ by the relation $Q = \frac{a^4 b^3}{c^2}$. The percentage error in $a, b$ and $c$ are $3\%$, $4\%$ and $5\%$ respectively. Then, the percentage error in $Q$ is:

  1. 66$\%$
  2. 43$\%$
  3. 34$\%$
  4. 14$\%$

Answer: (c)

Solution

Given $$Q = \frac{a^4 b^3}{c^2}$$ The relative error in $Q$ is given by $$\frac{\Delta Q}{Q} = 4 \frac{\Delta a}{a} + 3 \frac{\Delta b}{b} + 2 \frac{\Delta c}{c}$$ Multiplying by 100 to find the percentage error, we have $$\frac{\Delta Q}{Q} \times 100 = 4 \left( \frac{\Delta a}{a} \times 100 \right) + 3 \left( \frac{\Delta b}{b} \times 100 \right) + 2 \left( \frac{\Delta c}{c} \times 100 \right)$$ Substituting the given percentage errors, % error in $Q = 4 \times 3\% + 3 \times 4\% + 2 \times 5\%$ $$= 12\% + 12\% + 10\%$$ $$= 34\%$$

Question 34

Physics · Alternating Current · Single correct

In an a.c. circuit, voltage and current are given by: $V = 100 \sin(100t) \, \mathrm{V}$ and $I = 100 \sin\left(100t + \frac{\pi}{3}\right) \, \mathrm{mA}$ respectively. The average power dissipated in one cycle is:

  1. 5 W
  2. 10 W
  3. 2.5 W
  4. 25 W

Answer: (c)

Solution

Given $P_{avg} = V_{rms} I_{rms} \cos(\Delta \phi)$. $$= \frac{100}{\sqrt{2}} \times \frac{100 \times 10^{-3}}{\sqrt{2}} \times \cos\left(\frac{\pi}{3}\right)$$ $$= \frac{10^4}{2} \times \frac{1}{2} \times 10^{-3}$$ $$= \frac{10}{4} = 2.5 \, W$$

Question 35

Physics · Kinetic Theory · Single correct

The temperature of a gas having $2.0 \times 10^{25}$ molecules per cubic meter at $1.38 \, \mathrm{atm}$ (Given, $k = 1.38 \times 10^{-23} \, \mathrm{JK^{-1}}$) is:

  1. 500 K
  2. 200 K
  3. 100 K
  4. 300 K

Answer: (a)

Solution

Given the equation $PV = nRT$. We can express $PV$ as $PV = \frac{N}{N_A} RT$. Here, $N$ is the total number of molecules. The pressure $P$ is given by $P = \frac{N}{V} kT$. Substituting the values, we have: $$1.38 \times 1.01 \times 10^5 = 2 \times 10^{25} \times 1.38 \times 10^{-23} \times T$$ Simplifying, we get: $$1.01 \times 10^5 = 2 \times 10^2 \times T$$ Solving for $T$: $$T = \frac{1.01 \times 10^3}{2} \approx 500 \, \mathrm{K}$$

Question 36

Physics · Laws of Motion · Single correct

A stone of mass 900 g is tied to a string and moved in a vertical circle of radius 1 m making 10 rpm. The tension in the string, when the stone is at the lowest point is (if $\pi^2 = 9.8$ and $g = 9.8 \, \mathrm{m/s^2}$)

  1. 97 N
  2. 9.8 N
  3. 8.82 N
  4. 17.8 N

Answer: (b)

Solution

Given that $$m = 900 \mathrm{gm} = \frac{900}{1000} \mathrm{kg} = \frac{9}{10} \mathrm{kg}$$ $$r = 1 \, \mathrm{m}$$ $$\omega = \frac{2 \pi N}{60} = \frac{2 \pi (10)}{60} = \frac{\pi}{3} \, \mathrm{rad/sec}$$ $$T - mg = mr \omega^2$$ $$T = mg + mr \omega^2$$ $$= \frac{9}{10} \times 9.8 + \frac{9}{10} \times 1 \left( \frac{\pi}{3} \right)^2$$ $$= 8.82 + \frac{9}{10} \times \frac{\pi^2}{9}$$ $$= 8.82 + 0.98$$ $$= 9.80 \, \mathrm{N}$$

Question 37

Physics · Work, Energy and Power · Single correct

The bob of a pendulum was released from a horizontal position. The length of the pendulum is 10 m. If it dissipates 10$\%$ of its initial energy against air resistance, the speed with which the bob arrives at the lowest point is : [Use, $g : 10 \, \mathrm{ms^{-2}}$]

  1. $6\sqrt{5} \, \mathrm{ms^{-1}}$
  2. $5\sqrt{6} \, \mathrm{ms^{-1}}$
  3. $5\sqrt{5} \, \mathrm{ms^{-1}}$
  4. $2\sqrt{5} \, \mathrm{ms^{-1}}$

Answer: (a)

Solution

Given $\ell = 10 \, \mathrm{m}$. Initial energy $= mg\ell$. So, $\($ $\frac{9}{10}$ mg$\ell$ = $\frac{1}{2}$ mv^2 $\)$. Therefore, $\($ $\frac{9}{10}$ $\times$ 10 $\times$ 10 = $\frac{1}{2}$ v^2 $\)$. Solving for $v^2$, we get $v^2 = 180$. Thus, $v = \sqrt{180} = 6\sqrt{5} \, \mathrm{m/s}$.

Question 38

Physics · Ray Optics and Optical Instruments · Single correct

If the distance between object and its two times magnified virtual image produced by a curved mirror is 15 cm, the focal length of the mirror must be:

  1. 15 $\mathrm{cm}$
  2. -12 $\mathrm{cm}$
  3. -10 $\mathrm{cm}$
  4. $\frac{10}{3}$ $\mathrm{cm}$

Answer: (c)

Solution

Given the magnification $m = 2$, we have: $$m = \frac{-v}{u}$$ Substituting $v = 15 - u$, we get: $$2 = \frac{-(15 - u)}{-u}$$ Simplifying, we find: $$2u = 15 - u$$ $$3u = 15 \Rightarrow u = 5 \, \mathrm{cm}$$ Now, substituting back to find $v$: $$v = 15 - u = 15 - 5 = 10 \, \mathrm{cm}$$ Using the lens formula: $$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$$ Substitute the values: $$\frac{1}{f} = \frac{1}{10} + \frac{1}{(-5)} = \frac{1 - 2}{10} = \frac{-1}{10}$$ Thus, the focal length is: $$f = -10 \, \mathrm{cm}$$

Question 39

Physics · Moving Charges and Magnetism · Single correct

Two particles X and Y having equal charges are being accelerated through the same potential difference. Thereafter they enter normally in a region of uniform magnetic field and describes circular paths of radii $R_1$ and $R_2$ respectively. The mass ratio of X and Y is:

  1. $\left(\frac{R_2}{R_1}\right)^2$
  2. $\left(\frac{R_1}{R_2}\right)^2$
  3. $\frac{R_1}{R_2}$
  4. $\frac{R_2}{R_1}$

Answer: (b)

Solution

Given $$R = \frac{mv}{qB} = \frac{p}{qB} = \frac{\sqrt{2\, m (\mathrm{KE})}}{qB} = \frac{\sqrt{2mqV}}{qB}$$ We have $$R \propto \sqrt{m}$$ And $$m \propto R^2$$ Thus, $$\frac{m_1}{m_2} = \left(\frac{R_1}{R_2}\right)^2$$

Question 40

Physics · Wave Optics · Single correct

In Young's double slit experiment, light from two identical sources are superimposing on a screen. The path difference between the two lights reaching at a point on the screen is $\frac{7\lambda}{4}$. The ratio of intensity of fringe at this point with respect to the maximum intensity of the fringe is :

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

Answer: (a)

Solution

Given $\Delta x = \frac{7\lambda}{4}$. $$\phi = \frac{2\pi}{\lambda} \Delta x = \frac{2\pi}{\lambda} \times \frac{7\lambda}{4} = \frac{7\pi}{2}$$ $I = I_{\max} \cos^2 \left( \frac{\phi}{2} \right)$ $$\frac{I}{I_{\max}} = \cos^2 \left( \frac{\phi}{2} \right) = \cos^2 \left( \frac{7\pi}{2 \times 2} \right) = \cos^2 \left( \frac{7\pi}{4} \right)$$ $$= \cos^2 \left( 2\pi - \frac{\pi}{4} \right)$$ $$= \cos^2 \frac{\pi}{4}$$ $$= \frac{1}{2}$$

Question 41

Physics · Mechanical Properties of Fluids · Single correct

A small liquid drop of radius R is divided into 27 identical liquid drops. If the surface tension is T, then the work done in the process will be :

  1. 8$\pi$ R^2 T
  2. 3$\pi$ R^2 T
  3. $\frac{1}{8}$ $\pi$ R^2 T
  4. 4$\pi$ R^2 T

Answer: (a)

Solution

Volume constant $$\frac{4}{3} \pi R^3 = 27 \times \frac{4}{3} \times \pi r^3$$ $$R^3 = 27r^3$$ $$R = 3r$$ $$r = \frac{R}{3}$$ $$r^2 = \frac{R^2}{9}$$ Work done $= T \cdot \Delta A$ $$= 27 \, T \left(4 \pi r^2\right) - T 4 \pi R^2$$ $$= 27 \, T 4 \pi \frac{R^2}{9} - 4 \pi R^2 \, T$$ $$= 8 \pi R^2 \, T$$

Question 42

Physics · Work, Energy and Power · Single correct

A bob of mass ' $m$ ' is suspended by a light string of length ' $L$ '. It is imparted a minimum horizontal velocity at the lowest point A such that it just completes half circle reaching the top most position B. The ratio of kinetic energies $\frac{(\mathrm{K.E.})_A}{(\mathrm{K.E.})_B}$ is:

  1. 3 : 2
  2. 5 : 1
  3. 2 : 5
  4. 1 : 5

Answer: (b)

Solution

Apply energy conservation between A and B $$\frac{1}{2} m V_L^2 = \frac{1}{2} m V_H^2 + mg(2L)$$ Therefore, $V_L = \sqrt{5gL}$ So, $V_H = \sqrt{gL}$ $$\frac{(\mathrm{K.E})_A}{(\mathrm{K.E})_B} = \frac{\frac{1}{2} m (\sqrt{5gL})^2}{\frac{1}{2} m (\sqrt{gL})^2} = \frac{5}{1}$$

Question 43

Physics · Mechanical Properties of Solids · Single correct

A wire of length $L$ and radius $r$ is clamped at one end. If its other end is pulled by a force $F$, its length increases by $l$. If the radius of the wire and the applied force both are reduced to half of their original values keeping original length constant, the increase in length will become.

  1. 3 times
  2. 3/2 times
  3. 4 times
  4. 2 times

Answer: (d)

Solution

Given $$Y = \frac{stress}{strain}$$ $$Y = \frac{\frac{F}{\ell/2}}{\frac{\ell}{L}}$$ $$F = Y \pi r^2 \times \frac{\ell}{L} \cdots (i)$$ $$Y = \frac{\frac{F r/2}{\Delta \ell/2}}{L}$$ $$F = Y \frac{\Delta \ell}{L} \times 2 \times \frac{\pi r^2}{4}$$ From (i) $$Y \pi r^2 \frac{\ell}{L} = Y \frac{\Delta \ell}{L} \frac{\pi r^2}{2}$$ $$\Delta \ell = 2 \ell$$

Question 44

Physics · Gravitation · Single correct

A planet takes 200 days to complete one revolution around the Sun. If the distance of the planet from Sun is reduced to one fourth of the original distance, how many days will it take to complete one revolution?

  1. 25
  2. 50
  3. 100
  4. 20

Answer: (a)

Solution

Given $T^2 \propto r^3$. Therefore, $\($ $\frac{T_1^2}{r_1^3}$ = $\frac{T_2^2}{r_2^3}$ $\)$. Substituting the given values, $\($ $\frac{(200)^2}{r^3}$ = $\frac{T_2^2}{\left(\frac{r}{4}\right)^3}$ $\)$. Simplifying, $\($ $\frac{200 \times 200}{4 \times 4 \times 4}$ = T_2^2 $\)$. Solving for $T_2$, we get $\($ T_2 = $\frac{200}{4 \times 2}$ $\)$. Therefore, $T_2 = 25$ days.

Question 45

Physics · Electromagnetic Waves · Single correct

A plane electromagnetic wave of frequency 35 $\mathrm{MHz}$ travels in free space along the X-direction. At a particular point (in space and time) $\vec{E} = 9.6\hat{j} \, \mathrm{V/m}$. The value of magnetic field at this point is :

  1. $3.2$ $\times$ $10^{-8}$$\hat{k}$ $\mathrm{T}$
  2. $3.2$ $\times$ $10^{-8}$ $\hat{i}$ $\mathrm{T}$
  3. $9.6$ $\hat{j}$ $\mathrm{T}$
  4. $9.6$ $\times$ $10^{-8}$ $\hat{k}$ $\mathrm{T}$

Answer: (a)

Solution

Given $\($ $\frac{E}{B}$ = C $\)$ and $\($ $\frac{E}{B}$ = 3 $\times$ 10^8 $\)$. Therefore, $\($ B = $\frac{E}{3 \times 10^8}$ = $\frac{9.6}{3 \times 10^8}$ $\)$. Thus, $\($ B = 3.2 $\times$ 10^{-8} $\mathrm{T}$ $\)$. The direction of $\($ $\mathbf{\hat{B}}$ = $\mathbf{\hat{v}}$ $\times$ $\mathbf{\hat{E}}$ $\)$ is $\($ $\mathbf{\hat{i}}$ $\times$ $\mathbf{\hat{j}}$ = $\mathbf{\hat{k}}$ $\)$. So, $\($ $\mathbf{B}$ = 3.2 $\times$ 10^{-8} $\mathbf{\hat{k}}$ $\mathrm{T}$ $\)$.

Question 46

Physics · Current Electricity · Single correct

In the given circuit, the current in resistance $R_3$ is:

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

Answer: (a)

Solution

The equivalent resistance is given by $R_{eq} = 2\,\Omega + 2\,\Omega + 1\,\Omega = 5\,\Omega$. The current $i$ is calculated as $i = \frac{V}{R_{eq}} = \frac{10}{5} = 2\,A$. Current in resistance $R_3$ is calculated as follows: $$R_3 = 2 \times \left( \frac{4}{4 + 4} \right)$$ $$= 2 \times \frac{4}{8}$$ $$= 1\,A$$

Question 47

Physics · Motion in a Straight Line · Single correct

A particle is moving in a straight line. The variation of position ' $x$ ' as a function of time ' $t$ ' is given as $$x = (t^3 - 6t^2 + 20t + 15) \, \mathrm{m}.$$ The velocity of the body when its acceleration becomes zero is :

  1. 4 m/s
  2. 8 m/s
  3. 10 m/s
  4. 6 m/s

Answer: (b)

Solution

Given $x = t^3 - 6t^2 + 20t + 15$. Differentiate with respect to $t$: $$\frac{dx}{dt} = v = 3t^2 - 12t + 20$$ Differentiate again to find acceleration: $$\frac{dv}{dt} = a = 6t - 12$$ When $a = 0$, solve for $t$: $$6t - 12 = 0; \ t = 2 sec$$ At $t = 2 sec$, calculate $v$: $$v = 3(2)^2 - 12(2) + 20$$ $$v = 8 \, \mathrm{m/s}$$

Question 48

Physics · Kinetic Theory · Single correct

N moles of a polyatomic gas $(f = 6)$ must be mixed with two moles of a monoatomic gas so that the mixture behaves as a diatomic gas. The value of $N$ is:

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

Answer: (c)

Solution

Given the equation for $f_{eq}$: $$f_{eq} = \frac{n_1 f_1 + n_2 f_2}{n_1 + n_2}$$ For diatomic gas, $f_{eq} = 5$. $$5 = \frac{(N)(6) + (2)(3)}{N + 2}$$ Simplifying, we have: $$5N + 10 = 6N + 6$$ Solving for $N$: $$N = 4$$

Question 49

Physics · Atoms · Single correct

Given below are two statements:\ Statement I : Most of the mass of the atom and all its positive charge are concentrated in a tiny nucleus and the electrons revolve around it, is Rutherford's model.\ Statement II : An atom is a spherical cloud of positive charges with electrons embedded in it, is a special case of Rutherford's model.\ In the light of the above statements, choose the most appropriate from the options given below.

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

Answer: (c)

Solution

According to Rutherford atomic model, most of mass of atom and all its positive charge is concentrated in tiny nucleus and electron revolve around it. According to Thomson atomic model, atom is spherical cloud of positive charge with electron embedded in it. Hence, Statement I is true but statement II false.

Question 50

Physics · Electric Charges and Fields · Single correct

An electric field is given by $(6\hat{i} + 5\hat{j} + 3\hat{k}) \, \mathrm{N/C}$. The electric flux through a surface area $30\hat{i} \, \mathrm{m^2}$ lying in YZ-plane (in SI unit) is :

  1. 90
  2. 150
  3. 180
  4. 60

Answer: (c)

Solution

Given $\vec{E} = 6\hat{i} + 5\hat{j} + 3\hat{k}$ and $\vec{A} = 30\hat{i}$. The flux $\phi$ is given by the dot product $\vec{E} \cdot \vec{A}$. Therefore, $$\phi = (6\hat{i} + 5\hat{j} + 3\hat{k}) \cdot (30\hat{i})$$ $$\phi = 6 \times 30 = 180$$

Question 51

Physics · Mechanical Properties of Solids · Numerical

Two metallic wires P and Q have same volume and are made up of same material. If their area of cross sections are in the ratio 4 : 1 and force $F_1$ is applied to P, an extension of $\Delta l$ is produced. The force which is required to produce same extension in Q is $F_2$. The value of $\frac{F_1}{F_2}$ is

Answer: 16

Solution

Given $$Y = \frac{Stress}{Strain} = \frac{F/A}{\Delta \ell / \ell} = \frac{F \ell}{A \Delta \ell}$$ $$\Delta \ell = \frac{F \ell}{A Y}$$ $$V = A \ell \Rightarrow \ell = \frac{V}{A}$$ $$\Delta \ell = \frac{F V}{A^2 Y}$$ $Y$ and $V$ are the same for both the wires. $$\Delta \ell \propto \frac{F}{A^2}$$ $$\frac{\Delta \ell_1}{\Delta \ell_2} = \frac{F_1}{A_1^2} \times \frac{A_2^2}{F_2}$$ $$\Delta \ell_1 = \Delta \ell_2$$ $$F_1 A_2^2 = F_2 A_1^2$$ $$\frac{F_1}{F_2} = \frac{A_1^2}{A_2^2} = \left( \frac{4}{1} \right)^2 = 16$$

Question 52

Physics · Electromagnetic Induction · Numerical

A horizontal straight wire 5 m long extending from east to west falling freely at right angle to horizontal component of earth's magnetic field $0.60 \times 10^{-4} \, \mathrm{Wb} \, \mathrm{m}^{-2}$. The instantaneous value of emf induced in the wire when its velocity is $10 \, \mathrm{ms}^{-1}$ is _____ $\times 10^{-3} \, \mathrm{V}$

Answer: 3

Solution

Given $B_H = 0.60 \times 10^{-4} \, \mathrm{Wb/m^2}$. Induced emf $e = B_H v \ell$. $$e = 0.60 \times 10^{-4} \times 10 \times 5$$ $$= 3 \times 10^{-3} \, \mathrm{V}$$

Question 53

Physics · Atoms · Numerical

Hydrogen atom is bombarded with electrons accelerated through a potential different of $V$, which causes excitation of hydrogen atoms. If the experiment is being formed at $T = 0 \, \mathrm{K}$. The minimum potential difference needed to observe any Balmer series lines in the emission spectra will be $\frac{\alpha}{10} \, V$, where $\alpha$ =

Answer: 121

Solution

For minimum potential difference electron has to make transition from $n = 3$ to $n = 2$ state but first electron has to reach to $n = 3$ state from ground state. So, energy of bombarding electron should be equal to energy difference of $n = 3$ and $n = 1$ state. $$\Delta E = 13.6 \left[ 1 - \frac{1}{3^2} \right] e = \mathrm{eV}$$ $$\frac{13.6 \times 8}{9} = V$$ $$V = 12.09 \, \mathrm{V} \approx 12.1 \, \mathrm{V}$$ So, $\alpha = 121$

Question 54

Physics · Moving Charges and Magnetism · Numerical

A charge of $4.0\,\mu\mathrm{C}$ is moving with a velocity of $4.0 \times 10^6\,\mathrm{m\,s}^{-1}$ along the positive $y$-axis under a magnetic field $\mathbf{B}$ of strength $(2\hat{k})\,\mathrm{T}$. The force acting on the charge is $x\hat{i}\,\mathrm{N}$. The value of $x$ is

Answer: 32

Solution

Given $q = 4 \, \mu \mathrm{C}$, $\vec{v} = 4 \times 10^6 \hat{\jmath} \, \mathrm{m/s}$ and $\vec{B} = 2 \hat{k} \, \mathrm{T}$. The force $\vec{F}$ is given by $q(\vec{v} \times \vec{B})$. $$\vec{F} = 4 \times 10^{-6} \left( 4 \times 10^6 \hat{\jmath} \times 2 \hat{k} \right)$$ $$= 4 \times 10^{-6} \times 8 \times 10^6 \hat{\imath}$$ $$\vec{F} = 32 \hat{\imath} \, \mathrm{N}$$ Therefore, $x = 32$.

Question 55

Physics · Oscillations · Fill in the blank

A simple harmonic oscillator has an amplitude $A$ and time period $6\pi$ seconds. Assuming the oscillation starts from its mean position, the time required by it to travel from $x = A$ to $x = \frac{\sqrt{3}}{2}A$ will be $\frac{\pi}{x}$ s, where x = _____

Answer: 2

Solution

From phasor diagram particle has to move from P to Q in a circle of radius equal to amplitude of SHM. $$\cos \phi = \frac{\sqrt{3} A}{2 A} = \frac{\sqrt{3}}{2}$$ $$\phi = \frac{\pi}{6}$$ Now, $$\frac{\pi}{6} = \omega t$$ $$\frac{\pi}{6} = \frac{2\pi}{T} t$$ $$\frac{\pi}{6} = \frac{2\pi}{6\pi} t$$ $$t = \frac{\pi}{2}$$ So, $$x = 2$$

Question 56

Physics · Alternating Current · Numerical

In the given figure, the charge stored in $6\mu F$ capacitor, when points A and B are joined by a connecting wire is ______ $\mu C$.

Answer: 36

Solution

At steady state, the capacitor behaves as an open circuit and current flows in the circuit as shown in the diagram. $$R_{eq} = 9 \, \Omega$$ $$i = \frac{9 \, V}{9 \, \Omega} = 1 \, A$$ $$\Delta V_{6\Omega} = 1 \times 6 = 6 \, V$$ $$V_A = 3 \, V$$ So, the potential difference across $6 \, \mu F$ is $6 \, V$. Hence $$Q = C \Delta V$$ $$= 6 \times 6 \times 10^{-6} \, C$$ $$= 36 \, \mu C$$

Question 57

Physics · Wave Optics · Numerical

In a single slit diffraction pattern, a light of wavelength $6000\,\mathrm{\AA}$ is used. The distance between the first and third minima in the diffraction pattern is found to be $3\,\mathrm{mm}$ when the screen in placed $50\,\mathrm{cm}$ away from slits. The width of the slit is _____ $\times 10^{-4}\,\mathrm{m}$.

Answer: 2

Solution

For $n^{th}$ minima $$b \sin \theta = n \lambda$$ ($\lambda$ is small so $\sin \theta$ is small, hence $\sin \theta \simeq \tan \theta$) $$b \tan \theta = n \lambda$$ $$\frac{b}{D} y = n \lambda$$ $$\Rightarrow \; y_n = \frac{n \lambda D}{b} \; (Position of $n^{th}$ minima)$$ $B \rightarrow 1^{st}$ minima, $A \rightarrow 3^{rd}$ minima $$y_3 = \frac{3 \lambda D}{b}, \; y_1 = \frac{\lambda D}{b}$$ $$\Delta y = y_3 - y_1 = \frac{2 \lambda D}{b}$$ $$3 \times 10^{-3} = \frac{2 \times 6000 \times 10^{-10} \times 0.5}{b}$$ $$b = \frac{2 \times 6000 \times 10^{-10} \times 0.5}{3 \times 10^{-3}}$$ $$b = 2 \times 10^{-4} \, \mathrm{m}$$ $$x = 2$$

Question 58

Physics · Current Electricity · Numerical

In the given circuit, the current flowing through the resistance $20 \, \Omega$ is $0.3 \, \mathrm{A}$, while the ammeter reads $0.9 \, \mathrm{A}$. The value of $R_1$ is _____ $\Omega$.

Answer: 30

Solution

Given, $i_1 = 0.3 \, \mathrm{A}$, $i_1 + i_2 + i_3 = 0.9 \, \mathrm{A}$. So, $V_{AB} = i_1 \times 20\, \Omega = 20 \times 0.3 \, \mathrm{V} = 6 \, \mathrm{V}$. $$i_2 = \frac{6 \, \mathrm{V}}{15\, \Omega} = \frac{2}{5} \, \mathrm{A}$$ $$i_1 + i_2 + i_3 = \frac{9}{10} \, \mathrm{A}$$ $$\frac{3}{10} + \frac{2}{5} + i_3 = \frac{9}{10}$$ $$\frac{7}{10} + i_3 = \frac{9}{10}$$ $$i_3 = 0.2 \, \mathrm{A}$$ So, $i_3 \times R_1 = 6 \, \mathrm{V}$. $$(0.2)R_1 = 6$$ $$R_1 = \frac{6}{0.2} = 30\, \Omega$$

Question 59

Physics · Motion in a Plane · Fill in the blank

A particle is moving in a circle of radius 50 $\mathrm{\ cm}$ in such a way that at any instant the normal and tangential components of its acceleration are equal. If its speed at t = 0 is 4 $\mathrm{\ m/s}$, the time taken to complete the first revolution will be $\frac{1}{\alpha}$ [ 1 - $e^{-2\pi}$] $\mathrm{\ s}$, where $\alpha$ = .

Answer: 8

Solution

Given $|\vec{a}_c| = |\vec{a}_t|$. $$\frac{v^2}{r} = \frac{dv}{dt}$$ This implies $$\int_4^v \frac{dv}{v^2} = \int_0^t \frac{dt}{r}$$ Therefore, $$\left[ -\frac{1}{v} \right]_4^v = \frac{t}{r}$$ This gives $$-\frac{1}{v} + \frac{1}{4} = 2t$$ Thus, $$v = \frac{4}{1 - 8t} = \frac{ds}{dt}$$ Integrating, $$4 \int_0^t \frac{dt}{1 - 8t} = \int_0^s ds$$ Given $r = 0.5 \, \mathrm{m}$ and $s = 2\pi r = \pi$, we have $$4 \times \left[ \ln(1 - 8t) \right]_0^t = \pi$$ This simplifies to $$\frac{\ln(1 - 8t)}{-8} = -2\pi$$ Therefore, $$1 - 8t = e^{-2\pi}$$ Solving for $t$, $$t = \left(1 - e^{-2\pi}\right) \frac{1}{8} s$$ So, $\alpha = 8$

Question 60

Physics · System of Particles and Rotational Motion · Numerical

A body of mass 5 kg moving with a uniform speed $3\sqrt{2} \, \mathrm{ms}^{-1}$ in $X - Y$ plane along the line $y = x + 4$. The angular momentum of the particle about the origin will be _____ $\mathrm{kgm}^2 \mathrm{s}^{-1}$.

Answer: 60

Solution

Given the equation of the line: $$y - x - 4 = 0$$ $d_1$ is the perpendicular distance of the given line from the origin. $$d_1 = \left| \frac{-4}{\sqrt{1^2 + 1^2}} \right| \Rightarrow 2\sqrt{2} \, \mathrm{m}$$ So, $$|\vec{L}| = m v d_1 = 5 \times 3\sqrt{2} \times 2\sqrt{2} \, \mathrm{kg \, m^2/s}$$ $$= 60 \, \mathrm{kg \, m^2/s}$$

Chemistry

Question 61

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

The ascending acidity order of the following H atoms is

  1. C < D < B < A
  2. A < B < C < D
  3. A < B < D < C
  4. D < C < B < A

Answer: (a)

Solution

The stability of the conjugate base is proportional to acidic strength. The order is $\mathrm{C} < \mathrm{D} < \mathrm{B} < \mathrm{A}$.

Question 62

Chemistry · Biomolecules · Single correct

Match List I with List II \begin{tabular}{|l|l|} \hline \textbf{List I (Bio Polymer)} & \textbf{List II (Monomer)} \\ \hline A. Starch & I. nucleotide \\ \hline B. Cellulose & II. $\alpha$-glucose \\ \hline C. Nucleic acid & III. $\beta$-glucose \\ \hline D. Protein & IV. $\alpha$-amino acid \\ \hline \end{tabular} Choose the correct answer from the options given below :-

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

Answer: (d)

Solution

A-II, B-III, C-I, D-IV Fact based.

Question 63

Chemistry · Analytical Chemistry · Single correct

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

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

Answer: (d)

Solution

Ethanol $\rightarrow 15.9$ Phenol $\rightarrow 10$ M-Nitrophenol $\rightarrow 8.3$ P-Nitrophenol $\rightarrow 7.1$

Question 64

Chemistry · Amines · Single correct

Which of the following reaction is correct?

  1. $\mathrm{CH_3CH_2CH_2NH_2} \xrightarrow[\mathrm{H_2O}]{\mathrm{HNO_2^\circ C}} \mathrm{CH_3CH_2OH + N_2 + HCl}$

Answer: (b)

Solution

The reaction involves the addition of HI to the alkene. According to Markovnikov's rule, the iodine (I) will add to the more substituted carbon atom, resulting in the formation of the product shown.

Question 65

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

According to IUPAC system, the compound is named as

  1. Cyclohex-1-en-2-ol
  2. 1-Hydroxyhex-2-ene
  3. Cyclohex-1-en-3-ol
  4. Cyclohex-2-en-1-ol

Answer: (d)

Solution

Cyclohex-2-en-1-ol

Question 66

Chemistry · Co-ordination Compounds · Single correct

The correct IUPAC name of $\mathrm{K_2MnO_4}$ is

  1. Potassium tetraoxopermanganate (VI)
  2. Potassium tetraoxidomanganate (VI)
  3. Dipotassium tetraoxidomanganate (VII)
  4. Potassium tetraoxidomanganese (VI)

Answer: (b)

Solution

Given $\mathrm{K_2MnO_4}$. $2 + x - 8 = 0$ Therefore, $x = +6$. The oxidation state of Mn is $+6$. IUPAC Name = Potassium tetraoxidomanganate(VI)

Question 67

Chemistry · Analytical Chemistry · Single correct

A reagent which gives brilliant red precipitate with Nickel ions in basic medium is

  1. sodium nitroprusside
  2. neutral FeCl_3
  3. meta-dinitrobenzene
  4. dimethyl glyoxime

Answer: (d)

Solution

The reaction is given by: $$\mathrm{Ni^{2+} + 2dmg^- \rightarrow [Ni(dmg)_2]}$$ This results in a rosy red or bright red precipitate.

Question 68

Chemistry · Alcohols, Phenols and Ethers · Single correct

Phenol treated with chloroform in presence of sodium hydroxide, which further hydrolysed in presence of an acid results

  1. Salicyclic acid
  2. Benzene-1,2-diol
  3. Benzene-1, 3-diol
  4. 2-Hydroxybenzaldehyde

Answer: (d)

Solution

It is Reimer Tiemann Reaction

Question 69

Chemistry · Structure of Atom · Single correct

Match List I with List II \begin{tabular}{|l|l|} \hline \textbf{List-I} (Spectral Series for Hydrogen) & \textbf{List-II} ((Spectral Region/Higher Energy State) \\ \hline (A) Lyman & I. Infrared region \\ \hline (B) Balmer & II. UV region \\ \hline (C) Paschen & III. Infrared region \\ \hline (D) Pfund & IV. Visible region\\ \hline \end{tabular}

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

Answer: (c)

Solution

A - II, B - IV, C - III, D - I Fact based.

Question 70

Chemistry · Analytical Chemistry · Single correct

On passing a gas, 'X', through Nessler's reagent, a brown precipitate is obtained. The gas 'X' is

  1. $\mathrm{H_2S}$
  2. $\mathrm{CO_2}$
  3. $\mathrm{NH_3}$
  4. $\mathrm{Cl_2}$

Answer: (c)

Solution

Nessler's Reagent Reaction: $$2 \, \mathrm{K_2HgI_4} + \mathrm{NH_3} + 3\mathrm{KOH} \rightarrow \mathrm{HgO.Hg(NH_2)I} + 7\mathrm{KI} + 2\mathrm{H_2O}$$ (Nessler’s Reagent) (iodine of Millon’s base Brown precipitate)

Question 71

Chemistry · Amines · Single correct

The product A formed in the following reaction is:

Answer: (c)

Solution

The reaction involves the conversion of aniline to chlorobenzene. First, aniline ($\mathrm{C_6H_5NH_2}$) is treated with $\mathrm{NaNO_2}$ and $\mathrm{HCl}$ at $0^\circ \mathrm{C}$ to form a diazonium salt ($\mathrm{C_6H_5N_2^+Cl^-}$). This is followed by a Sandmeyer reaction using $\mathrm{Cu_2Cl_2}$ to replace the diazonium group with a chlorine atom, resulting in chlorobenzene ($\mathrm{C_6H_5Cl}$).

Question 72

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

Identify the reagents used for the following conversion

  1. A = $\mathrm{LiAlH_4}$, B = $\mathrm{NaOH_{(aq)}}$, C = $\mathrm{NH_2 - NH_2/KOH}$, ethylene glycol
  2. A = $\mathrm{LiAlH_4}$, B = $\mathrm{NaOH_{(alc)}}$, C = $\mathrm{Zn/HCl}$
  3. A = $\mathrm{DIBAL-H}$, B = $\mathrm{NaOH_{(aq)}}$, C = $\mathrm{NH_2 - NH_2/KOH}$, ethylene glycol
  4. A = $\mathrm{DIBAL-H}$, B = $\mathrm{NaOH_{(alc)}}$, C = $\mathrm{Zn/HCl}$

Answer: (d)

Solution

The reaction sequence involves three main steps. First, the ester group is selectively reduced to an aldehyde using DIBAL-H. This is followed by an intramolecular aldol condensation facilitated by alcoholic NaOH, leading to the formation of a cyclic compound with an aldehyde group. Finally, Clemmensen reduction using Zn/HCl removes the carbonyl group, resulting in the formation of the final product.

Question 73

Chemistry · The d-and f-Block Elements · Single correct

Which of the following acts as a strong reducing agent? (Atomic number : Ce = 58, Eu = 63, Gd = 64, Lu = 71)

  1. $\mathrm{Lu}^{3+}$
  2. $\mathrm{Gd}^{3+}$
  3. $\mathrm{Eu}^{2+}$
  4. $\mathrm{Ce}^{4+}$

Answer: (c)

Solution

For $\mathrm{Eu}^{+2}$, the electron configuration is $[\mathrm{Xe}]4f^7 6s^0$. When $\mathrm{Eu}^{+3}$ is formed, it loses one electron: $[\mathrm{Xe}]4f^7 6s^0 \rightarrow \mathrm{Eu}^{+3} + 1e^-$. The resulting configuration is $[\mathrm{Xe}]4f^6 6s^0$.

Question 74

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

Chromatographic technique/s based on the principle of differential adsorption is/are\ A. Column chromatography\ B. Thin layer chromatography\ C. Paper chromatography\ Choose the most appropriate answer from the options given below:

  1. B only
  2. A only
  3. A $\&$ B only
  4. C only

Answer: (c)

Question 75

Chemistry · The d-and f-Block Elements · Single correct

Which of the following statements are correct about Zn, Cd and Hg? A. They exhibit high enthalpy of atomization as the d-subshell is full. B. Zn and Cd do not show variable oxidation state while Hg shows +I and +II. C. Compounds of Zn, Cd and Hg are paramagnetic in nature. D. Zn, Cd and Hg are called soft metals. Choose the most appropriate from the options given below:

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

Answer: (a)

Solution

Q11 (A) $\mathrm{Zn}$, $\mathrm{Cd}$, $\mathrm{Hg}$ exhibit lowest enthalpy of atomization in respective transition series. (C) Compounds of $\mathrm{Zn}$, $\mathrm{Cd}$ and $\mathrm{Hg}$ are diamagnetic in nature.

Question 76

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

The element having the highest first ionization enthalpy is

  1. Si
  2. Al
  3. N
  4. C

Answer: (c)

Solution

Al < Si < C < N; IE_1 order.

Question 77

Chemistry · Haloalkanes and Haloarenes · Single correct

Alkyl halide is converted into alkyl isocyanide by reaction with

  1. NaCN
  2. NH_4CN
  3. KCN
  4. AgCN

Answer: (d)

Solution

Covalent character of $\mathrm{AgCN}$.

Question 78

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

Which one of the following will show geometrical isomerism?

Answer: (c)

Solution

Due to unsymmetrical.

Question 79

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

Given below are two statements:\ Statement I: Fluorine has most negative electron gain enthalpy in its group.\ Statement II: Oxygen has least negative electron gain enthalpy in its group.\ In the light of the above statements, choose the most appropriate from the options given below.

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

Answer: (d)

Solution

Statement-1 is false because chlorine has most negative electron gain enthalpy in its group.

Question 80

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

Anomalous behaviour of oxygen is due to its

  1. Large size and high electronegativity
  2. Small size and low electronegativity
  3. Small size and high electronegativity
  4. Large size and low electronegativity

Answer: (c)

Solution

Fact Based.

Question 81

Chemistry · Chemical Bonding and Molecular Structure · Numerical

The total number of anti bonding molecular orbitals, formed from 2s and 2p atomic orbitals in a diatomic molecule is

Answer: 4

Solution

Antibonding molecular orbital from $2s = 1$ Antibonding molecular orbital from $2p = 3$ Total $= 4$

Question 82

Chemistry · Analytical Chemistry · Numerical

The oxidation number of iron in the compound formed during brown ring test for $\mathrm{NO}_3^-$ ion is

Answer: 1

Solution

The complex is $[\mathrm{Fe(H_2O)_5(NO)]^{2+}}$. The oxidation number of $\mathrm{Fe}$ is $+1$.

Question 83

Chemistry · Equilibrium · Numerical

The following concentrations were observed at 500 K for the formation of $NH_3$ from $N_2$ and $H_2$. At equilibrium: $[N_2] = 2 \times 10^{-2} \, \mathrm{M}$, $[H_2] = 3 \times 10^{-2} \, \mathrm{M}$ and $[NH_3] = 1.5 \times 10^{-2} \, \mathrm{M}$. Equilibrium constant for the reaction is

Answer: 417

Solution

Given the equilibrium constant expression: $$K_C = \frac{[\mathrm{NH_3}]^2}{[\mathrm{N_2}][\mathrm{H_2}]^3}$$ Substitute the given concentrations: $$K_C = \frac{(1.5 \times 10^{-2})^2}{(2 \times 10^{-2}) \times (3 \times 10^{-2})^3}$$ Calculate the value: $$K_C = 417$$

Question 84

Chemistry · Solutions · Numerical

Molality of 0.8M $\mathrm{H}_2\mathrm{SO}_4$ solution (density $1.06 \, \mathrm{g} \, \mathrm{cm}^{-3}$) is _______ $\times 10^{-3}$ m.

Answer: 815

Solution

Given the formula for molality: $$m = \frac{M \times 1000}{d_{sol} \times 1000 - M \times Molar mass_{solute}}$$ The calculated molality is $815 \times 10^{-3} \, m$.

Question 85

Chemistry · Some Basic Concepts of Chemistry · Numerical

If 50 $\mathrm{mL}$ of 0.5 $\mathrm{M}$ oxalic acid is required to neutralise 25 $\mathrm{mL}$ of NaOH solution, the amount of NaOH in 50 $\mathrm{mL}$ of given NaOH solution is ______$\mathrm{g}$.

Answer: 4

Solution

Equivalent of Oxalic acid = Equivalents of NaOH $$50 \times 0.5 \times 2 = 25 \times M \times 1$$ $$M_{NaOH} = 2\, M$$ $$W_{NaOH} in 50\, ml$ $ = 2 \times 50 \times 40 \times 10^{-3}\, g = 4\, g$$

Question 86

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Numerical

The total number of 'Sigma' and Pi bonds in 2-formylhex-4-enoic acid is

Answer: 22

Solution

The molecule shown has a total of 22 bonds.

Question 87

Chemistry · Chemical Kinetics and Nuclear Chemistry · Numerical

The half-life of radioisotopic bromine - 82 is 36 hours. The fraction which remains after one day is $\underline{\hspace{0.6cm}}\times 10^{-2}$. (Given antilog 0.2006 = 1.587)

Answer: 63

Solution

Half life of bromine-82 = 36 hours $$t_{1/2} = \frac{0.693}{K}$$ $$K = \frac{0.693}{36} = 0.01925 \, \mathrm{hr}^{-1}$$ First order reaction kinetic equation $$t = \frac{2.303}{K} \log \frac{a}{a-x}$$ $$\log \frac{a}{a-x} = \frac{t \times K}{2.303} (t = 1 \, \mathrm{day} = 24 \, \mathrm{hr})$$ $$\log \frac{a}{a-x} = \frac{24 \, \mathrm{hr} \times 0.01925 \, \mathrm{hr}^{-1}}{2.303}$$ $$\log \frac{a}{a-x} = 0.2006$$ $$\frac{a}{a-x} = anti log(0.2006)$$ $$\frac{a}{a-x} = 1.587$$ If $a = 1$ $$\frac{1}{1-x} = 1.587 \Rightarrow 1-x = 0.6301 = Fraction remain after one day$$

Question 88

Chemistry · Thermodynamics · Fill in the blank

Standard enthalpy of vapourisation for $\mathrm{CCl_4}$ is $30.5\,\mathrm{kJ\,mol^{-1}}$. Heat required for vapourisation of $284\,\mathrm{g}$ of $\mathrm{CCl_4}$ at constant temperature is $\underline{\hspace{1cm}}\,\mathrm{kJ}$. (Given molar mass in $\mathrm{g\,mol^{-1}}$; $\mathrm{C}=12$, $\mathrm{Cl}=35.5$)

Answer: 56

Solution

Given $\Delta H^0_{vap} \ \mathrm{CCl_4} = 30.5 \, \mathrm{kJ/mol}$. Mass of $\mathrm{CCl_4} = 284 \, \mathrm{gm}$. Molar mass of $\mathrm{CCl_4} = 154 \, \mathrm{g/mol}$. Moles of $\mathrm{CCl_4} = \frac{284}{154} = 1.844 \, \mathrm{mol}$. $\Delta H^0_{vap}$ for 1 mole $= 30.5 \, \mathrm{kJ/mol}$. $\Delta H^0_{vap}$ for 1.844 mol $= 30.5 \times 1.844 = 56.242 \, \mathrm{kJ}$.

Question 89

Chemistry · Electrochemistry · Numerical

A constant current was passed through a solution of $\mathrm{AuCl}_4^-$ ion between gold electrodes. After a period of 10.0 minutes, the increase in mass of cathode was 1.314 g. The total charge passed through the solution is ____ $\times$ $10^{-2}$ $\mathrm{F}$. (Given atomic mass of $\mathrm{Au} = 197$)

Answer: 2

Solution

Given $\frac{W}{E}=\frac{\text{charge}}{1\,\mathrm{F}}$. $1.314\times\frac{197}{3}=\frac{Q}{1\,\mathrm{F}}$ $Q=2\times10^{-2}\,\mathrm{F}$

Question 90

Chemistry · Chemical Bonding and Molecular Structure · Numerical

The total number of molecules with zero dipole moment among $\mathrm{CH}_4$, $\mathrm{BF}_3$, $\mathrm{H}_2\mathrm{O}$, $\mathrm{HF}$, $\mathrm{NH}_3$, $\mathrm{CO}_2$ and $\mathrm{SO}_2$ is

Answer: 3

Solution

Molecules with zero dipole moment are $\mathrm{CO_2}$, $\mathrm{CH_4}$, $\mathrm{BF_3}$.