JEE Main 7 April 2025 Shift 1 question paper with solutions

JEE Main 7 April 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 · Limits and Derivatives · Single correct

$\lim_{x \to 0^+} \frac{\tan\left(5x^{\frac{1}{3}}\right)\log_e\left(1+3x^2\right)}{\left(\tan^{-1}\left(3\sqrt{x}\right)\right)^2\left(e^{5x^{\frac{4}{3}}}-1\right)}$ is equal to

  1. $\frac{1}{15}$
  2. 1
  3. $\frac{1}{3}$
  4. $\frac{5}{3}$

Answer: (c)

Solution

The limit to evaluate is given by $$\lim_{x \to 0} \left( \frac{\tan(5x^{1/3})}{5x^{1/3}} \right) \cdot \left( \frac{(3\sqrt{x})^2}{(\tan^{-1} 3\sqrt{x})^2} \right) \cdot \left( \frac{\ell\,(1 + 3x^2)}{3x^2} \right) \cdot \left( \frac{5x^{4/3}}{e^{5x^4} - 1} \right) \times \frac{5x^{1/3} \cdot 3x^2}{5x^{4/3} \cdot 9x}$$ The result of this limit is $$= \frac{1}{3}$$

Question 2

Maths · Three Dimensional Geometry · Single correct

If the shortest distance between the lines $\frac{x-1}{2} = \frac{y-2}{3} = \frac{z-3}{4}$ and $\frac{x}{1} = \frac{y}{\alpha} = \frac{z-5}{1}$ is $\frac{5}{\sqrt{6}}$, then the sum of all possible values of $\alpha$ is

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

Answer: (d)

Solution

For line $L_1$: $\($ $\frac{x-1}{2}$ = $\frac{y-2}{3}$ = $\frac{z-3}{4}$ $\)$. For line $L_2$: $\($ $\frac{x}{1}$ = $\frac{y}{\alpha}$ = $\frac{z-5}{1}$ $\)$. The vector $\($ $\vec{x}$ = $\begin{vmatrix}$ $\hat{i}$ & $\hat{j}$ & $\hat{k}$ $\\$ 2 & 3 & 4 $\\$ 1 & $\alpha$ & 1 $\end{vmatrix}$ = $\hat{i}$(3 - 4$\alpha$) - $\hat{j}$(-2) + $\hat{k}$(2$\alpha$ - 3) $\)$. The shortest distance (S.D.) is given by: $$ S.D. = \frac{\vec{BA} \cdot \vec{n}}{\| \vec{n} \|} = \frac{(\hat{i} + 2\hat{j} - 2\hat{k}) \cdot \vec{n}}{\| \vec{n} \|} $$ This implies: $$ 6(13 - 8\alpha)^2 = 25 \left( (4\alpha - 3)^2 + (2\alpha - 3)^2 + 16 \right) $$ Simplifying gives: $$ 6 \left( 64\alpha^2 - 280\alpha + 169 \right) = 25 \left( 20\alpha^2 - 36\alpha + 34 \right) $$ Further simplification leads to: $$ 116\alpha^2 + 348\alpha - 164 = 0 $$ Solving for $\($ $\alpha$ $\)$: $$ \alpha_1 + \alpha_2 = \frac{-348}{116} = -3 $$

Question 3

Maths · Applications of Derivatives · Single correct

Let $x = -1$ and $x = 2$ be the critical points of the function $f(x) = x^3 + ax^2 + b \log_c |x| + 1, x \neq 0$. Let $m$ and $M$ respectively be the absolute minimum and the absolute maximum values of $f$ in the interval $\left[-2, -\frac{1}{2}\right]$. Then $|M + m|$ is equal to (Take $\log_c 2 = 0.7$):

  1. 21.1
  2. 19.8
  3. 22.1
  4. 20.9

Answer: (a)

Solution

Given $f(x) = x^2 + ax^2 + b \ln |x| + 1$, $x \neq 0$. Differentiating, we have $$f'(x) = 3x^2 + 2ax + \frac{b}{x}$$ Evaluating at $x = -1$, $$f'(-1) = 3 - 2a - b = 0$$ Evaluating at $x = -2$, $$f'(-2) = 12 + 4a - \frac{b}{2} = 0$$ Solving these equations, we find $$a = -\frac{9}{2}, b = 12$$ Thus, $$f'(x) = 3x^2 - 9x + \frac{12}{x} = \frac{3(x+1)(x+2)^2}{x}$$ Maximum at $n = -1$. Substituting back, $$f(x) = x^2 - \frac{9}{2}x^2 + 12 \ln |x| + 1$$ At $x = -1$, $$f(-1) = -1 - \frac{9}{2} + 1 = -\frac{9}{2}$$ Maximum value $M = -4.5$. Minimum value at $x = -2$. At $x = -2$, $$f(-2) = -8 - 18 + 12 \ln 2 + 1$$ Thus, $$m = -25 + 12 \ln 2 = -16.6$$ The absolute value of the sum is $$|M + m| = 21.1$$

Question 4

Maths · Binomial Theorem · Single correct

The remainder when $((64)^{(64)})^{(64)}$ is divided by 7 is equal to

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

Answer: (b)

Solution

Let $N = ((64)^{64})^{64}$. $N = (64)^{64^2}$. $N = (1 + 63)^{64^2}$, let $64^2 = n$. Expanding by binomial $$N = (1 + 63)^n = 1 + nC_1 63 + nC_2 (63)^2 + \ldots$$ $$= 1 + 63 \lambda = 1 + 7(9 \lambda)$$ Remainder when divided by 7 is 1

Question 5

Maths · Conic Sections · Single correct

Let P be the parabola, whose focus is $(-2,1)$ and directrix is $2x + y + 2 = 0$. Then the sum of the ordinates of the points on P, whose abscissa is $-2$, is

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

Answer: (a)

Solution

Equation of parabola Given $$(x+2)^2 + (y-1)^2 = \left(\frac{2x+y+2}{\sqrt{5}}\right)^2$$ We have: $$5\left[(x+2)^2 + (y-1)^2\right] = (2x+y+2)^2$$ Put $x = -2$, then: $$5(y-1)^2 = (y-2)^2$$ Expanding both sides: $$5(y^2 - 2y + 1) = y^2 - 4y + 4$$ Simplifying gives: $$\Rightarrow 4y^2 - 6y + 1 = 0 \Rightarrow y_1 + y_2 = \frac{3}{2}$$

Question 6

Maths · Differential Equations · Single correct

Let $y = y(x)$ be the solution curve of the differential equation $$x \left(x^2 + e^x\right) \, dy + \left(e^x(x - 2)y - x^3\right) \, dx = 0, \; x > 0$$ passing through the point (1, 0). Then $y(2)$ is equal to:

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

Answer: (d)

Solution

Given the equation $x \left( x^2 + e^x \right) \frac{dy}{dx} + \left( e^x (x-2)y - x^3 \right) dx = 0$. Rewriting, we have $x \left( x^2 + e^x \right) \frac{dy}{dx} + e^x (x-2)y = x^3$. This simplifies to $$\frac{dy}{dx} + \frac{e^x (x-2)}{x(x^2 + e^x)} y = \frac{x^2}{x^2 + e^x}.$$ The integrating factor (I.F.) is $e^{\int \frac{e^x (x-2)}{x(x^2 + e^x)} dx} = e^{\int \frac{e^x}{x^2 + e^x} dx}$. Let $1 + \frac{e^x}{x^2} = t \Rightarrow x^2 e^x - e^x 2x dx = x^4 dx = dt$. Thus, $$I.F. = e^{\ln \left( 1 + \frac{e^x}{x^2} \right)} = 1 + \frac{e^x}{x^2}.$$ Now, $$y \left( 1 + \frac{e^x}{x^2} \right) = \int \frac{x^2}{x^2 + e^x} \cdot \frac{x^2 + e^x}{x^2} dx + C.$$ Therefore, $$y \left( 1 + \frac{e^x}{x^2} \right) = x + C.$$ Passing through $(1,0)$ gives $C = -1$. Thus, $$y = \frac{x-1}{1 + \frac{e^x}{x^2}}.$$ Evaluating $y(2)$, we have $$y(2) = \frac{1}{1 + \frac{e^2}{4}} = \frac{4}{4 + e^2}.$$

Question 7

Maths · Permutations and Combinations · Single correct

From a group of 7 batsmen and 6 bowlers, 10 players are to be chosen for a team, which should include atleast 4 batsmen and atleast 4 bowlers. One batsmen and one bowler who are captain and vice-captain respectively of the team should be included. Then the total number of ways such a selection can be made, is

  1. 165
  2. 155
  3. 145
  4. 135

Answer: (b)

Solution

7 Batsmen and 6 Bowlers. To select 10 players including at least 4 Batsmen and 4 Bowlers. Captain and vice-captain already selected. Number of ways is $$\binom{6}{5} \times \binom{5}{3} + \binom{6}{4} \times \binom{5}{4} + \binom{6}{3} \times \binom{5}{5}$$ $$= 6 \times 10 + 15 \times 5 + 20 \times 1$$ $$= 60 + 75 + 20 = 155$$

Question 8

Maths · Trigonometric Functions · Single correct

If for $\theta \in \left[ -\frac{\pi}{3}, 0 \right]$, the points $(x, y) = \left( 3 \tan \left( \theta + \frac{\pi}{3} \right), 2 \tan \left( \theta + \frac{\pi}{6} \right) \right)$ lie on $xy + \alpha x + \beta y + \gamma = 0$, then $\alpha^2 + \beta^2 + \gamma^2$ is equal to:

  1. 80
  2. 72
  3. 96
  4. 75

Answer: (d)

Solution

Given $$x = 3 \left( \frac{\tan \theta + \sqrt{3}}{1 - \sqrt{3} \tan \theta} \right)$$ $$x - \sqrt{3} \tan \theta = 3 \tan \theta + 3 \sqrt{3}$$ $$\tan \theta = \frac{x - 3 \sqrt{3}}{3 + \sqrt{3} x} \cdots (1)$$ $$2 \left( \frac{\tan \theta + \frac{1}{\sqrt{3}}}{1 - \frac{\tan \theta}{\sqrt{3}}} \right) = y$$ $$2(\sqrt{3} \tan \theta + 1) = y(\sqrt{3} - \tan \theta) \cdots$$ Using (1) and (2) $$2 \left( \frac{x - 3 \sqrt{3}}{\sqrt{3} + x} + 1 \right) = y \left( \sqrt{3} - \frac{x - 3 \sqrt{3}}{\sqrt{3} + x} \right)$$ $$2 \sqrt{3} (x - 3 \sqrt{3} + x + \sqrt{3}) = y(3(\sqrt{3} + x) - x + 3 \sqrt{3})$$ $$4 \sqrt{3} x - 12 = y(2x + 6 \sqrt{3})$$ $$xy - 2 \sqrt{3} x + 3 \sqrt{3} y - 6 = 0$$ $$\Rightarrow \alpha = -2 \sqrt{3}, \beta = 3 \sqrt{3}, \gamma = -6$$ $$\alpha^2 + \beta^2 + \gamma^2 = 12 + 27 + 36 = 75$$

Question 9

Maths · Conic Sections · Single correct

Let $C_1$ be the circle in the third quadrant of radius 3, that touches both coordinate axes. Let $C_2$ be the circle with centre $(1, 3)$ that touches $C_1$ externally at the point $(\alpha, \beta)$. If $(\beta - \alpha)^2 = \dfrac{m}{n}$, $\gcd(m, n) = 1$, then $m + n$ is equal to :

  1. 9
  2. 13
  3. 22
  4. 31

Answer: (c)

Solution

Let $C_1$ and $C_2$ have centres $A(-3, -3)$ and $B(1, 3)$. $AB = \sqrt{16 + 36} = 2\sqrt{13}$ $r_1 = 3$ and $r_2 = 2\sqrt{13} - 3$ $P(\alpha, \beta), \alpha = \frac{r_1(1) + r_2(-3)}{r_1 + r_2}, \beta = \frac{r_1(3) + r_2(-3)}{r_1 + r_2}$ $\alpha = \frac{3 - 3(2\sqrt{13} - 3)}{2\sqrt{13}}, \beta = \frac{18 - 6\sqrt{13}}{2\sqrt{13}}$ $\left( \beta - \alpha \right)^2 = \left( \frac{6}{2\sqrt{13}} \right)^2$ $\left( \beta - \alpha \right)^2 = \left( \frac{6}{2\sqrt{13}} \right)^2, \; m + n = 22$

Question 10

Maths · Integrals · Single correct

The integral $$\int_{0}^{\pi} \frac{(x+3)\sin x}{1+3\cos^2 x} \, dx$$ is equal to :

  1. $\frac{\pi}{\sqrt{3}} (\pi + 1)$
  2. $\frac{\pi}{\sqrt{3}} (\pi + 2)$
  3. $\frac{\pi}{3\sqrt{3}} (\pi + 6)$
  4. $\frac{\pi}{2\sqrt{3}} (\pi + 4)$

Answer: (c)

Solution

Given $$I = \int_0^\pi \frac{(x+3) \sin x}{1 + 3 \cos^2 x} \, dx$$ We have $$I = \int_0^\pi \frac{(\pi - x + 3) \sin x}{(1 + 3 \cos^2 x)} \, dx$$ Thus, $$2I = \int_0^\pi \frac{(\pi + 6) \sin x \cdot dx}{(1 + 3 \cos^2 x)} = 2 \int_0^{\pi/2} \frac{(\pi + 6) \sin x}{(1 + 3 \cos^2 x)}$$ Therefore, $$I = \int_0^{\pi/2} \frac{(\pi + 6) \sin x \cdot dx}{(1 + 3 \cos^2 x)} = \frac{\pi}{3\sqrt{3}} (\pi + 6)$$ Let $\sqrt{3} \cos x = t$ and $\sqrt{3} \sin x = dt$.

Question 11

Maths · Complex Numbers and Quadratic Equations · Single correct

Among the statements (S1) : The set $\{z \in \mathbb{C} - \{-i\} : |z| = 1 \text{ and } \frac{z-i}{z+i} \text{ is purely real}\}$ contains exactly two elements, and (S2) : The set $\{z \in \mathbb{C} - \{-1\} : |z| = 1 \text{ and } \frac{z-1}{z+1} \text{ is purely imaginary}\}$ contains infinitely many elements.

  1. both are incorrect
  2. only (S1) is correct
  3. only (S2) is correct
  4. both are correct

Answer: (c)

Solution

Given $S_1: |z| = 1$, $\frac{z-i}{z+i} = \frac{\overline{z}+i}{\overline{z}-i}$. This implies $$(z-i)(\overline{z}-i) = (z+i)(\overline{z}+i)$$ $$|z|^2 - i(z + \overline{z}) - 1 = |z|^2 + i(z + \overline{z}) - 1$$ $$i(z + \overline{z}) = 0$$ $$z + \overline{z} = 2 \cos \theta = 0 \Rightarrow \cos \theta = 0$$ $$z = 0 + 0i, \ |z| \neq 1$$ For $S_1: \frac{z-1}{z+1} + \frac{\overline{z}-1}{\overline{z}+1} = 0$, $$(z-1)(\overline{z}+1) + (z+1)(\overline{z}-1) = 0$$ This implies $$|z|^2 + (z - \overline{z}) - 1 + |z|^2 + (\overline{z} - z) - 1 = 0$$ $$|z|^2 = 1$$

Question 12

Maths · Statistics · Single correct

The mean and standard deviation of 100 observations are 40 and 5.1, respectively. By mistake one observation is taken as 50 instead of 40. If the correct mean and the correct standard deviation are $\mu$ and $\sigma$ respectively, then $10(\mu + \sigma)$ is equal to

  1. 445
  2. 451
  3. 447
  4. 449

Answer: (d)

Solution

Actual means $= \mu = \frac{100(40) - 50 + 40}{100}$. $$\mu = 40 - \frac{1}{10} = 39.9$$ Incorrect variance $$(5.1)^2 = \frac{\sum x_i^2}{100} - \left(\bar{x}\right)^2$$ $$\sum x_i^2 = 100 \times (40^2) + 100(5.1)^2$$ $$\sum x_i^2 = 16 \times 10^4 + (5.1)^2 \times 100 = 162601$$ $$\sigma^2 = \frac{\sum x_i^2 - 50^2 + 40^2}{100} - (\mu)^2$$ $$\sigma^2 = 1617.01 - (39.9)^2 = 25$$ $$\sigma = 5$$ $$10(\mu + \sigma) = 10(39.9 + 5)$$ $$= 10 \times 44.9 = 449$$

Question 13

Maths · Sequences and Series · Single correct

Let $x_1, x_2, x_3, x_4$ be in a geometric progression. 2, 7, 9, 5 are subtracted respectively from $x_1, x_2, x_3, x_4$ then the resulting numbers are in an arithmetic progression. Then the value of $\frac{1}{24}(x_1 x_2 x_3 x_4)$ is:

  1. 72
  2. 18
  3. 36
  4. 216

Answer: (d)

Solution

Given $x_1, x_2, x_3, x_4 \rightarrow G.P.$ Let $a, ar, ar^2, ar^3 \rightarrow G.P.$ Now $a - 2, ar - 7, a^2 - 9, ar^3 - 5 \rightarrow A.P.$ $2(ar - 7) = a - 2 + ar^2 - 9 \ldots (i)$ $2(a^2 - 9) = ar - 7 + ar^3 - 5 \ldots (ii)$ Solving $r = 2, a = -3$ Therefore, Product $= x_1, x_2, x_3, x_4 = a^4 r^6 = 81 \times 64$ Solving $r = 2, a = -3$ Therefore, Product $= x_1, x_2, x_3, x_4 = a^4 r^6 = 81 \times 64$

Question 14

Maths · Complex Numbers and Quadratic Equations · Single correct

Let the set of all values of $p \in \mathbb{R}$, for which both the roots of the equation $x^2 - (p+2)x + (2p+9) = 0$ are negative real numbers, be the interval $(\alpha, \beta]$. Then $\beta - 2\alpha$ is equal to

  1. 0

Answer: (a)

Solution

Using location of roots: (i) $D \geq 0$ (ii) $\frac{-b}{2a} 0$ $$(p + 2)^2 - 4(2p + 9) \geq 0$$ $$(p + 4)(p - 8) \geq 0 p + 2 0$$ Intersection $p \in \left( -\frac{9}{2}, -4 \right]$ Therefore, $\beta - 2\alpha = -4 + 9 = 5$

Question 15

Maths · Determinants · Single correct

Let A be a 3 $\times$ 3 matrix such that $|\mathrm{adj}(\mathrm{adj}(A))| = 81$. If $$S = \left\{ n \in \mathbb{Z} : \left( |\mathrm{adj}(\mathrm{adj}(A))| \right)^{\frac{(n-1)^2}{x}} = |A| (3n^2 - 5n - 4) \right\}$$ , then $\sum_{n \in S} |A^{(n^2 + n)}|$ is equal to

  1. 866
  2. 750
  3. 820
  4. 732

Answer: (d)

Solution

Given $|adj(adj(adj A))| = 81$. Therefore, $|adj A|^4 = 81$. This implies $|adj A| = 3$. Hence, $|A|^2 = 3$ and $|A| = \sqrt{3}$. Now, $\($ $\left$( |A|^4 $\right$)^{$\frac{(n-1)^2}{2}$} = |A|^{n^2 - 5n - 4} $\)$. This gives $2(n-1)^2 = 3n^2 - 5n - 4$. Simplifying, $2n^2 - 4n + 2 = 3n^2 - 5n - 4$. Thus, $n^2 - n - 6 = 0$. Factoring, $(n-3)(n+2) = 0$. Therefore, $n = 3, -2$. The sum $\sum_{n \in S} |A^{n^2 + n}| = |A^2| + |A^{12}| = 3 + 36 = 3 + 729 = 732$.

Question 16

Maths · Applications of Integrals · Single correct

If the area of the region bounded by the curves $y = 4 - \frac{x^2}{4}$ and $y = \frac{x-4}{2}$ is equal to $\alpha$, then $6\alpha$ equals

  1. 250
  2. 210
  3. 240
  4. 220

Answer: (a)

Solution

Area is given by $$\int_{-6}^{4} \left\{ \left( 4 - \frac{x^2}{4} \right) - \left( \frac{x - 4}{2} \right) \right\} \, dx$$ which simplifies to $$\int_{-6}^{4} \left\{ -\frac{x^2}{4} - \frac{x - 6}{2} \right\} \, dx$$ Calculating, we find $$\alpha = -\frac{x^3}{12} - 4 + \frac{x^2}{2} + 6x \bigg|_{-6}^{4} = \frac{125}{3}$$ Therefore, $$6\alpha = 250$$

Question 17

Maths · Determinants · Single correct

Let the system of equations: \[ \begin{aligned} 2x + 3y + 5z &= 9 \\ 7x + 3y - 2z &= 8 \\ 12x + 3y - (4+\lambda)z &= 16 - \mu \end{aligned} \] have infinitely many solutions. Then the radius of the circle centred at $(\lambda, \mu)$ and touching the line $4x = 3y$ is

  1. $\frac{17}{5}$
  2. $\frac{7}{5}$
  3. 7
  4. $\frac{21}{5}$
Solution

Given the determinant equation: $$\begin{vmatrix} 2 & 3 & 5 \\ 7 & 3 & -2 \\ 12 & 3 & -(\lambda + 4) \end{vmatrix} = 0$$ Expanding the determinant, we have: $$12(-21) - 3(-39) - (\lambda + 4)(-15) = 0$$ Simplifying, we get: $$-252 + 117 + 15(1 + 4) = 0$$ This simplifies to: $$15\lambda + 177 - 252 = 0$$ Solving for $\lambda$, we find: $$15\lambda - 75 = 0 \implies \lambda = 5$$ Next, consider the determinant: $$\begin{vmatrix} 9 & 3 & 5 \\ 8 & 3 & -2 \\ 16 - \mu & 3 & -9 \end{vmatrix} = 0 \implies \begin{vmatrix} 1 & 0 & 7 \\ \mu - 8 & 0 & 7 \\ 16 - \mu & 3 & -9 \end{vmatrix} = 0$$ Expanding, we have: $$7 - 7(\mu - 8) = 0 \implies 1 - (\mu - 8) = 0 \implies \mu = 9$$ Thus, the centre of the circle is $(5, 9)$. The radius is the length of the perpendicular from the centre $(5, 9)$: $$\begin{vmatrix} 20 - 27 \\ 5 \end{vmatrix} = \frac{7}{5}$$

Question 18

Maths · Three Dimensional Geometry · Single correct

Let the line L pass through (1, 1, 1) and intersect the lines $\frac{x-1}{2} = \frac{y+1}{3} = \frac{z-1}{4}$ and $\frac{x-3}{1} = \frac{y-4}{2} = \frac{z}{1}$. Then, which of the following points lies on the line L?

  1. (4, 22, 7)
  2. (5, 4, 3)
  3. (10, -29, -50)
  4. (7, 15, 13)

Answer: (d)

Solution

Dr's of AC implies $2\lambda, 3\lambda - 2, 4\lambda$. Dr's of BC implies $\mu + 2, 2\mu + 3, \mu - 1$. $$\frac{\mu + 2}{2\lambda} = \frac{2\mu + 3}{3\lambda - 2} = \frac{\mu - 1}{4\lambda}$$ implies $2(\mu + 2) = \mu - 1$ implies $\mu = -5$. Therefore, Dr's of BC implies $3, 7, 6$. The equation of L implies $$\frac{x - 1}{3} = \frac{y - 1}{7} = \frac{z - 1}{6}$$ $(7, 15, 13)$ satisfies.

Question 19

Maths · Vector Algebra · Single correct

Let the angle $\theta$, $0 < \theta < \frac{\pi}{2}$ between two unit vectors $\hat{a}$ and $\hat{b}$ be $\sin^{-1}\left(\frac{\sqrt{65}}{9}\right)$. If the vector $\vec{c} = 3\hat{a} + 6\hat{b} + 9(\hat{a} \times \hat{b})$, then the value of $9(\vec{c} \cdot \hat{a}) - 3(\vec{c} \cdot \hat{b})$ is

  1. 31
  2. 27
  3. 29
  4. 24

Answer: (c)

Solution

Given $\vec{c} = 3 \vec{a} + 6 \vec{b} + 9 (\vec{a} \times \vec{b})$. Since $\sin^{-1}\left(\frac{\sqrt{65}}{9}\right) \Rightarrow \sin \theta = \frac{\sqrt{65}}{9}$, it follows that $\cos \theta = \frac{4}{9}$. Calculate $\vec{c} \cdot \vec{a} = 3 |\vec{a}|^2 + 6 \vec{a} \cdot \vec{b} = 3 + \frac{6 \cdot 4}{9} = \frac{51}{9}$. Next, $\vec{c} \cdot \vec{a} = 3 \vec{a} \cdot \vec{b} + 6 |\vec{b}|^2 = \frac{3 \cdot 4}{9} + 6 = \frac{22}{3}$. Therefore, $9 (\vec{c} \cdot \vec{a}) - 3 (\vec{c} \cdot \vec{b}) = 51 - 22 = 29$.

Question 20

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

Let ABC be the triangle such that the equations of lines AB and AC be $3y - x = 2$ and $x + y = 2$, respectively, and the points B and C lie on x-axis. If P is the orthocentre of the triangle ABC, then the area of the triangle PBC is equal to

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

Answer: (d)

Solution

Equation of Altitude AP: $x = 1$. Equation of Altitude BP: $y - 0 = 1(x + 2)$. Therefore, $x = 1$ and $x - y + 2 = 0$. Point $P(1, 3)$. Area of $\triangle PBC = \frac{1}{2} \times 4 \times 3 = 6$.

Question 21

Maths · Continuity and Differentiability · Numerical

The number of points of discontinuity of the function $f(x) = \left[ \frac{x^2}{2} \right] - \left[ \sqrt{x} \right]$, $x \in [0, 4]$, where $[\cdot]$ denotes the greatest integer function is

Answer: 8

Solution

Check for $\left[ \frac{x^2}{2} \right]$ and $[\sqrt{x}]$ becomes integers. $\{0, 1, \sqrt{2}, 2, \sqrt{6}, \sqrt{8}, \sqrt{10}, \sqrt{12}, \sqrt{14}, 4\}$ Continuous at $0^+$, continuous at $4^-$ $$\left[ \frac{x^2}{2} \right] = [\sqrt{x}],$$ occurs at $x = \sqrt{2}$ Therefore, not continuous.

Question 22

Maths · Sets · Fill in the blank

The number of relations on the set $A = \{1, 2, 3\}$ containing at most 6 elements including $(1, 2)$, which are reflexive and transitive but not symmetric, is

Answer: 5

Solution

Given $A = \{1, 2, 3\}$. The elements $(1, 1), (2, 2), (3, 3), (1, 2) \in R$. Remaining elements are $(2, 1), (2, 3), (1, 3), (3, 1), (3, 2)$. (1) If the relation contains exactly 4 elements, there is 1 way. (2) If the relation contains exactly 5 elements, it can be $(1, 3), (3, 2)$, which gives 2 ways. (3) If the relation contains exactly 6 elements, it can be $((2, 3), (1, 3)), ((1, 3), (3, 2)), ((3, 1), (3, 2))$, which gives 3 ways. Therefore, the total is 6 ways.

Question 23

Maths · Conic Sections · Numerical

Consider the hyperbola $\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$ having one of its focus at $P(-3, 0)$. If the latus rectum through its other focus subtends a right angle at $P$ and $a^2 b^2 = \alpha \sqrt{2} - \beta$, $\alpha, \beta \in \mathbb{N}$.

Answer: 1944

Solution

Given $f_1 \equiv (-ae, 0) \equiv P(-3, 0)$ and $ae = 3$. We have $\tan 45^\circ = \frac{b^2/a}{2ae}$. Therefore, $2ae = \frac{b^2}{a}$. This implies $b^2 = 6a$. Also, $a^2 e^2 = a^2 + b^2$. Thus, $9 = a^2 + 6a$. Solving $a^2 + 6a - 9 = 0$, we get $a = -3 \pm 3\sqrt{2} = -3(1 \pm \sqrt{2})$. Therefore, $a^2 b^2 = a^2 \cdot 6a = 6a^3 = 6(135\sqrt{2} - 189)$. Let $\alpha = 810$ and $\beta = 1134$. Thus, $\alpha + \beta = 1944$.

Question 24

Maths · Matrices · Numerical

The number of singular matrices of order 2, whose elements are from the set $\{$ 2, 3, 6, 9$\}$ is

Answer: 36

Solution

Given $\($ $\begin{vmatrix}$ a & d $\\$ b & c $\end{vmatrix}$ = ad - bc $\Rightarrow$ ad = bc $\)$ Case-I Exactly 1 number is used $\($ $\Rightarrow$ $\)$ All singular $\($ = $\binom{4}{1}$ $\)$ Case-II Exactly 2 numbers are used $\($ $\Rightarrow$ $\binom{4}{2}$ $\times$ 2 $\times$ 2 $\)$ Case-III Exactly 3 numbers are used None will be singular Case-IV Exactly 4 numbers are used $\($ ad = bc $\)$ $\($ $\Rightarrow$ 2 $\times$ 9 = 3 $\times$ 6 $\)$ $\($ $\begin{vmatrix}$ 9 & - $\\$ - & 2 $\end{vmatrix}$ $\Rightarrow$ $\binom{4}{1}$ $\times$ 21 $\)$ Total $\($ = 36 $\)$

Question 25

Maths · Sets · Numerical

For $n \geq 2$, let $S_n$ denote the set of all subsets of $\{1, 2, \ldots, n\}$ with no two consecutive numbers. For example $\{1, 3, 5\} \in S_6$, but $\{1, 2, 4\} \notin S_6$. Then $n(S_5)$ is equal to

Answer: 13

Solution

Given the set $A = \{1, 2, 3, 4, 5, \ldots, n\}$. The number of subsets having $r$ elements such that no two are consecutive is $= n-r+1 C_r$. For $n = 5$, the number of ways is $= {6 \choose r}$. Subsets having no element $= 1$. Subsets having exactly 1 element $= {5 \choose 1} = 5$. Subsets having exactly 2 elements $= {4 \choose 2} = 6$. Subsets having exactly 3 elements $= {3 \choose 3} = 1$. Therefore, $5 + 6 + 1 + 1 = 13$.

Physics

Question 26

Physics · Waves · Single correct

Two harmonic waves moving in the same direction superimpose to form a wave $x = a \cos(1.5t) \cos(50.5t)$ where $t$ is in seconds. Find the period with which they beat (close to nearest integer)

  1. 6 $\,$ $\mathrm{s}$
  2. 4 $\,$ $\mathrm{s}$
  3. 1 $\,$ $\mathrm{s}$
  4. 2 $\,$ $\mathrm{s}$

Answer: (d)

Solution

The given equation can be written as $$x = \frac{a}{2} \cos [1.5 + 50.5] t + \frac{a}{2} \cos [50.5 - 1.5]$$ $$x = \frac{a}{2} \cos [52t] + \frac{a}{2} \cos [49t]$$ Here, $2 \pi f_1$ and $2 \pi f_2 = 49$ $$f_1 = \frac{52}{2 \pi}, \; f_2 = \frac{49}{2 \pi}$$ Therefore, $f_{Beat} = f_1 - f_2 = \frac{3}{2 \pi} \; Hz$ Thus, $T_{Beat} = \frac{1}{f_{Beat}} = \frac{2 \pi}{3} \; sec$ $$= 2.09 \; sec \approx 2 \; sec$$

Question 27

Physics · Electromagnetic Waves · Single correct

Two plane polarized light waves combine at a certain point whose electric field components are $$E_1 = E_0 \sin \omega t$$ $$E_2 = E_0 \sin \left( \omega t + \frac{\pi}{3} \right)$$ Find the amplitude of the resultant wave.

  1. 0.9 E
  2. E_0
  3. 1.7E_0
  4. 3.4E_0

Answer: (c)

Solution

Given $$\mathbf{E} = \sqrt{(E_0)^2 + (E_0)^2 + 2\,(E_0)(E_0)\cos\frac{\pi}{3}}$$ We have: $$\mathbf{E} = \sqrt{2E_0^2 + E_0^2} = \sqrt{3}E_0 = 1.73E_0$$

Question 28

Physics · Current Electricity · Single correct

A wire of resistance $R$ is bent into a triangular pyramid as shown in figure with each segment having same length. The resistance between points $A$ and $B$ is $R/n$. The value of $n$ is :

  1. 16
  2. 14
  3. 10
  4. 12

Answer: (d)

Solution

As a balanced Wheatstone bridge is formed, the equivalent resistance between A and B can be written as $$\frac{1}{R_{AB}} = \frac{1}{2r} + \frac{1}{2r} + \frac{1}{r} = \frac{2}{r}$$ Therefore, $$R_{AB} = \frac{R}{12}$$

Question 29

Physics · Moving Charges and Magnetism · Single correct

Uniform magnetic fields of different strengths ($B_1$ and $B_2$), both normal to the plane of the paper exist as shown in the figure. A charged particle of mass $m$ and charge $q$, at the interface at an instant, moves into the region 2 with velocity $v$ and returns to the interface. It continues to move into region 1 and finally reaches the interface. What is the displacement of the particle during this movement along the interface? (Consider the velocity of the particle to be normal to the magnetic field and $B_2 > B_1$)

  1. $\frac{mv}{qB_1} \left(1 - \frac{B_2}{B_1}\right) \times 2$
  2. $\frac{mv}{qB_1} \left(1 - \frac{B_1}{B_2}\right)$
  3. $\frac{mv}{qB_1} \left(1 - \frac{B_2}{B_1}\right)$
  4. $\frac{mv}{qB_1} \left(1 - \frac{B_1}{B_2}\right) \times 2$

Answer: (d)

Solution

As $\vec{v}$ is $\perp$ to $\vec{B}$, so charge particle will move in circular path, whose radius is given by $$R = \frac{mv}{qB}$$ Starting point $\rightarrow$ A Ending point $\rightarrow$ C Therefore, Net displacement $=$ AC $$AC = CD - AD$$ $$AC = \frac{2mv}{qB_1} - \frac{2mv}{qB_2}$$ $$AC = \frac{2mv}{qB_1} \left[ 1 - \frac{B_1}{B_2} \right]$$

Question 30

Physics · Electromagnetic Waves · Single correct

If $\epsilon_0$ denotes the permittivity of free space and $\Phi_E$ is the flux of the electric field through the area bounded by the closed surface, then dimension of $\left( \epsilon_0 \frac{d\Phi_E}{dt} \right)$ are that of:

  1. Electric field
  2. Electric potential
  3. Electric charge
  4. Electric current

Answer: (d)

Solution

We know that the formula for displacement current is given by $$i_d = \varepsilon_0 \frac{d\phi_\varepsilon}{dt}$$

Question 31

Physics · System of Particles and Rotational Motion · Single correct

A rod of length 5 L is bent right angle keeping one side length as 2 L. The position of the centre of mass of the system: (Consider L = 10 $\mathrm{cm}$)

  1. 2$\hat{i}$ + 3$\hat{j}$
  2. 3$\hat{i}$ + 7$\hat{j}$
  3. 5$\hat{i}$ + 8$\hat{j}$
  4. 4$\hat{i}$ + 9$\hat{j}$

Answer: (d)

Solution

The center of mass (COM) of the system is calculated as follows. For the x-coordinate of the COM: $$x_{com} = \frac{2m(10) + 3m(0)}{2m + 3m} = 4 \, cm$$ For the y-coordinate of the COM: $$y_{com} = \frac{5m}{2m + 3m} = 9 \, cm$$ Therefore, the position vector of the COM is: $$\vec{r}_{com} = 4\hat{i} + 9\hat{j}$$

Question 32

Physics · Magnetism and Matter · Single correct

The percentage increase in magnetic field (B) when space within a current carrying solenoid is filled with magnesium (magnetic susceptibility $\chi_{mg} = 1.2 \times 10^{-5}$) is:

  1. $\frac{6}{5} \times 10^{-3}\%$
  2. $\frac{5}{6} \times 10^{-5}\%$
  3. $\frac{5}{6} \times 10^{-4}\%$
  4. $\frac{5}{3} \times 10^{-5}\%$

Answer: (a)

Solution

The percentage change in $B$ is given by $$\frac{B_{new} - B_{old}}{B_{old}} \times 100\%$$ Starting with $$\frac{\mu ni - \mu_0 ni}{\mu_0 ni} \times 100\% = \frac{(\mu - \mu_0)}{\mu_0} \times 100\%$$ This simplifies to $$\frac{(\mu_0 \mu_r - \mu_0)}{\mu_0} \times 100\%$$ Which further simplifies to $$(\mu_r - 1) \times 100\%$$ This is equal to $$\chi_n \times 100\%$$ Finally, we have $$= 1.2 \times 10^{-3}\%$$

Question 33

Physics · Ray Optics and Optical Instruments · Single correct

A lens having refractive index 1.6 has focal length of 12 cm, when it is in air. Find the focal length of the lens when it is placed in water. (Take refractive index of water as 1.28)

  1. 355 mm
  2. 288 mm
  3. 555 mm
  4. 655 mm

Answer: (b)

Solution

As we know, $$\frac{1}{f} = \left[ \frac{\mu_L}{\mu_m} - 1 \right] \left[ \frac{1}{R_1} - \frac{1}{R_2} \right]$$ For air $\mu_m = 1$ $$\frac{1}{12} = [1.6 - 1] \left[ \frac{1}{R_1} - \frac{1}{R_2} \right]$$ $$\frac{1}{12} = \frac{6}{10} \left[ \frac{1}{R_1} - \frac{1}{R_2} \right]$$ $$\left[ \frac{1}{R_1} - \frac{1}{R_2} \right] = \frac{10}{72}$$ For water $$\frac{1}{f} = \left[ \frac{1.6}{1.28} - 1 \right] \left[ \frac{10}{72} \right] = \frac{32}{128} \times \frac{10}{72}$$ $$\frac{1}{f} = \frac{1}{4} \times \frac{10}{72}$$ $$f = 28.8 \, \mathrm{cm}$$ $$f = 288 \, \mathrm{mm}$$

Question 34

Physics · Alternating Current · Single correct

An ac current is represented as \[ i=5\sqrt{2}+10\cos\left(650\pi t+\frac{\pi}{6}\right)\ \mathrm{A}. \] The rms value of the current is \[ \underline{\hspace{2cm}}. \]

  1. 50 Amp
  2. 100 Amp
  3. 10 Amp
  4. 5$\sqrt{2}$ Amp

Answer: (c)

Solution

Given $i = 5\sqrt{2} + 10 \cos \left(650 \pi t + \frac{\pi}{6}\right)$. $i^2 = 50 + 100 \cos^2 \left(650 \pi t + \frac{\pi}{6}\right) + (2)(5\sqrt{2})(10) \cos \left(650 \pi t + \frac{\pi}{6}\right)$. $\langle i^2 \rangle = 50 + \frac{100}{2} + 0$. $\langle i^2 \rangle = 100$. $\langle i \rangle = 10 Amp$.

Question 35

Physics · Ray Optics and Optical Instruments · Single correct

Two thin convex lenses of focal length 30 cm and 10 cm are placed coaxially, 10 cm apart. The power of this combination is:

  1. 5 D
  2. 1 D
  3. 20 D
  4. 10 D

Answer: (d)

Solution

Given $f_1 = 30 \, \mathrm{cm}$, $f_2 = 10 \, \mathrm{cm}$. $$\frac{1}{f_{eq}} = \frac{1}{f_1} + \frac{1}{f_2} - \frac{d}{f_1 f_2}, \; d = distance between lens$$ $$\frac{1}{f_{eq}} = \frac{1}{0.3} + \frac{1}{0.1} - \frac{0.1}{(0.3)(0.1)}$$ $$\frac{1}{f_{eq}} = 1 + 0.1$$ $$\frac{1}{f_{eq}} = 1$$ Power $= \frac{1}{f_{eq}} = 10 \, \mathrm{D}$

Question 36

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

In the following circuit, the reading of the ammeter will be (Take Zener breakdown voltage $= 4 \, \mathrm{V}$)

  1. $24 \, \mathrm{mA}$
  2. $80 \, \mathrm{mA}$
  3. $10 \, \mathrm{mA}$
  4. $16 \, \mathrm{mA}$

Answer: (c)

Solution

Given $V_1 = \frac{400}{100+400} \times 12 \, \mathrm{V} = \frac{4}{5} \times 12 = \frac{48}{5} \, \mathrm{V}$. Here, $V_1 > V_z$, ($V_z = Zener Voltage$). So, Zener breakdown will take place. Therefore, the voltage across $400 \, \Omega$ will be $4 \, \mathrm{V}$. The current $I = \frac{4}{400} \, \mathrm{A} = \frac{1}{100} \, \mathrm{A} = 10 \, \mathrm{mA}$.

Question 37

Physics · Motion in a Plane · Single correct

Two projectiles are fired from ground with same initial speeds from same point at angles $(45^\circ + \alpha)$ and $(45^\circ - \alpha)$ with horizontal direction. The ratio of their times of flights is

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

Answer: (d)

Solution

Given $\theta_1 = 45 + \alpha$ and $\theta_2 = 45 - \alpha$. The time of flight $T$ is given by $$T = \frac{2v \sin \theta}{g}$$ For $T_1$: $$T_1 = \sin(45 + \alpha)$$ For $T_2$: $$T_2 = \sin(45 - \alpha)$$ Simplifying further, $$T_1 = \frac{1}{\sqrt{2}} \cos \alpha + \frac{1}{\sqrt{2}} \sin \alpha$$ $$T_2 = \frac{1}{\sqrt{2}} \cos \alpha - \frac{1}{\sqrt{2}} \sin \alpha$$ Therefore, $$T_1 = \frac{\cos \alpha + \sin \alpha}{\cos \alpha - \sin \alpha} = \frac{1 + \tan \alpha}{1 - \tan \alpha}$$

Question 38

Physics · Kinetic Theory · Single correct

Match the List-I with List-II. \begin{tabular}{|l|l|}\hline\textbf{LIST-I} & \textbf{LIST-II} \\\hlineA. Triatomic rigid gas & I. $\dfrac{C_P}{C_V} = \dfrac{5}{3}$ \\[10pt]\hlineB. Diatomic non-rigid gas & II. $\dfrac{C_P}{C_V} = \dfrac{7}{5}$ \\[10pt]\hlineC. Monoatomic gas & III. $\dfrac{C_P}{C_V} = \dfrac{4}{3}$ \\[10pt]\hlineD. Diatomic rigid gas & IV. $\dfrac{C_P}{C_V} = \dfrac{9}{7}$ \\[10pt]\hline\end{tabular} Choose the correct answer from the options given below

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

Answer: (a)

Solution

Given $\gamma = 1 + \frac{2}{f}$. (1) $f = 6$, Triatomic rigid gas $f = 7$, Diatomic non-rigid gas $f = 5$, Diatomic rigid gas $f = 3$, monoatomic rigid gas $\gamma = 1 + \frac{2}{6} = \frac{4}{3}$ (Triatomic) $\gamma = 1 + \frac{2}{7} = \frac{9}{7}$ (Diatomic, non-rigid) $\gamma = 1 + \frac{2}{5} = \frac{7}{5}$ (Diatomic, rigid) $\gamma = 1 + \frac{2}{3} = \frac{5}{3}$ (Monoatomic, rigid) A-III, B-IV, C-I, D-II

Question 39

Physics · Laws of Motion · Single correct

A cubic block of mass $m$ is sliding down on an inclined plane at $60^\circ$ with an acceleration of $\frac{g}{2}$, the value of coefficient of kinetic friction is

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

Answer: (a)

Solution

Given the forces acting on the block, we have the equation: $$mg \sin 60^\circ - \mu mg \cos 60^\circ = ma$$ Substituting the given acceleration $a = \frac{g}{2}$, we get: $$g \sin 60^\circ - \mu g \cos 60^\circ = \frac{g}{2}$$ Solving for $\mu$, we have: $$\frac{\sqrt{3}}{2} - \frac{\mu}{2} = \frac{1}{2}$$ Therefore, $$\mu = \sqrt{3} - 1$$

Question 40

Physics · Atoms · Single correct

In a hydrogen like ion, the energy difference between the $2^{nd}$ excitation energy state and ground is $108.8 \, \mathrm{eV}$. The atomic number of the ion is

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

Answer: (d)

Solution

Given $\Delta E = 13.6 z^2 \left[ \frac{1}{n_1^2} - \frac{1}{n_2^2} \right]$. $$ (13.6) z^2 \left[ \frac{1}{1^2} - \frac{1}{9} \right] = 108.8 $$ $$ \frac{(13.6)(8)}{9} (z^2) = 108.8 $$ $$ z = 3 $$

Question 41

Physics · Atoms · Single correct

For a hydrogen atom, the ratio of the largest wavelength of Lyman series to that of the Balmer series is.

  1. 5 : 36
  2. 5 : 27
  3. 3 : 4
  4. 27 : 5

Answer: (b)

Solution

For the Lyman series, when $n = 2$ to $n = 1$, we have: $$\frac{1}{\lambda_1} = R \left[ \frac{1}{1^2} - \frac{1}{2^2} \right] = \frac{3R}{4}$$ Thus, $$\lambda_1 = \frac{4}{3R} ...(1)$$ For the Balmer series, when $n = 3$ to $n = 2$, we have: $$\frac{1}{\lambda_2} = R \left[ \frac{1}{2^2} - \frac{1}{3^2} \right] = \frac{5R}{36}$$ Thus, $$\lambda_2 = \frac{36}{5R}$$ Then, $$\frac{\lambda_1}{\lambda_2} = \frac{5}{27}$$

Question 42

Physics · Moving Charges and Magnetism · Single correct

A particle of charge $q$, mass $m$ and kinetic energy $E$ enters in magnetic field perpendicular to its velocity and undergoes a circular arc of radius $(r)$. Which of the following curves represents the variation of $r$ with $E$?

Answer: (d)

Solution

Given the equations of motion in a magnetic field, we have: $$\frac{mv^2}{r} = qvB$$ Solving for $mv$, we get: $$mv = qBr$$ The kinetic energy $E$ is given by: $$E = \frac{1}{2} mv^2$$ Substituting $mv = qBr$ into the expression for $E$: $$E = \frac{1}{2} m \left( \frac{q^2 B^2 r^2}{m^2} \right) = \frac{q^2 B^2 r^2}{2m}$$ This simplifies to: $$E = \left( \frac{q^2 B^2}{2m} \right) r^2$$ The graph shows that $r^2 \propto E$.

Question 43

Physics · Work, Energy and Power · Single correct

An object of mass 1000 g experiences a time dependent force $\vec{F} = \left( 2t \hat{i} + 3t^2 \hat{j} \right)$ N. The power generated by the force at time $t$ is:

  1. $(2t^2 + 3t^3) \, \mathrm{W}$
  2. $(2t^2 + 18t^3) \, \mathrm{W}$
  3. $(3t^3 + 5t^5) \, \mathrm{W}$
  4. $(2t^3 + 3t^5) \, \mathrm{W}$

Answer: (d)

Solution

Given $\vec{F} = (2t \hat{i} + 3t \hat{j}) \mathrm{N}$. $m = 1000 \mathrm{gm} = 1 \mathrm{kg}$. $\vec{F} = m \vec{a}$, $\vec{a} = 2t \hat{i} + 3t^2 \hat{j}$. $\frac{d \vec{v}}{dt} = 2t \hat{i} + 3t^2 \hat{j}$. $\vec{v} = t^2 \hat{i} + t^3 \hat{j}$. Power, $P = \vec{F} \cdot \vec{v}$. $$P = (2t \hat{i} + 3t^2 \hat{j}) \cdot (t^2 \hat{i} + t^3 \hat{j})$$ $$P = (2t^3 + 3t^5) \mathrm{W}$$

Question 44

Physics · Mechanical Properties of Solids · Single correct

Two wires A and B are made of same material having ratio of lengths $\frac{L_A}{L_B} = \frac{1}{3}$ and their diameters ratio $\frac{d_A}{d_B} = 2$. If both the wires are stretched using same force, what would be the ratio of their respective elongations?

  1. 1 : 6
  2. 1 : 12
  3. 3 : 4
  4. 1 : 3

Answer: (b)

Solution

Given $\frac{L_A}{L_B} = \frac{1}{3}$ and $\frac{d_A}{d_B} = 2$. $$\frac{\Delta L_A}{\Delta L_B} = \frac{F_A L_A}{A_A Y_A} and \frac{\Delta L_B}{\Delta L_B} = \frac{F_B L_B}{A_B Y_B}$$ Given, $F_A = F_B$ and $Y_A = Y_B$. $$\frac{\Delta L_A}{\Delta L_B} = \frac{F_A L_A}{A_A Y_A} = \left(\frac{L_A}{L_B}\right) \left(\frac{A_B}{A_A}\right)$$ $$\frac{\Delta L_A}{\Delta L_B} = \left(\frac{L_A}{L_B}\right) \left(\frac{\frac{\pi}{4} d_B^2}{\frac{\pi}{4} d_A^2}\right) = \left(\frac{L_A}{L_B}\right) \left(\frac{d_B}{d_A}\right)^2$$ $$\frac{\Delta L_A}{\Delta L_B} = \left(\frac{1}{3}\right) \left(\frac{1}{2}\right)^2 = \frac{1}{12}$$

Question 45

Physics · Electrostatic Potential and Capacitance · Single correct

Two charges $q_1$ and $q_2$ are separated by a distance of 30 cm. A third charge $q_3$ initially at 'C' as shown in the figure, is moved along the circular path of radius 40 cm from C to D. If the difference in potential energy due to movement of $q_3$ from C to D is given by $\frac{q_3 K}{4 \pi \varepsilon_0}$, the value of $K$ is:

  1. $8q_2$
  2. $6q_2$
  3. $8q_1$
  4. $6q_1$

Answer: (a)

Solution

Potential at C $$V_C = \frac{kq_1}{0.4} + \frac{kq_2}{0.5}$$ Potential at D $$V_D = \frac{kq_1}{0.4} + \frac{kq_2}{0.1}$$ $$\Delta U = (V_D - V_C)(q_3) = \left(\frac{kq_2}{0.1} - \frac{kq_2}{0.5}\right)(q_3)$$ $$\Delta U = 8kq_2q_3 = \frac{8q_2q_3}{4\pi \varepsilon_0}$$

Question 46

Physics · System of Particles and Rotational Motion · Numerical

A, B and C are disc, solid sphere and spherical shell respectively with same radii and masses. These masses are placed as shown in figure. The moment of inertia of the given system about PQ is $\frac{X}{15} I$, where $I$ is the moment of inertia of the disc about its diameter. The value of $x$ is _______.

Answer: 199

Solution

All bodies have same mass and same radius. A $\rightarrow$ Disc B $\rightarrow$ Solid sphere C $\rightarrow$ Spherical shell and, I = $\frac{MR^2}{4}$ I_{PQ} = $\frac{MR^2}{4}$ + $\left$( $\frac{2}{5}$ MR^2 + MR^2 $\right$) + $\left$( $\frac{2}{3}$ MR^2 + MR^2 $\right$) I_{PQ} = $\frac{15MR^2 + 24MR^2 + 60MR^2 + 40MR^2 + 60MR^2}{60}$ I_{PQ} = $\frac{199}{60}$ MR^2 = $\frac{199}{15}$ $\left$( $\frac{MR^2}{4}$ $\right$) = $\frac{199}{15}$ I

Question 47

Physics · Alternating Current · Subjective

For ac circuit shown in figure, $R = 100 \, \mathrm{k\Omega}$ and $C = 100 \, \mathrm{pF}$ and the phase difference between $V_{in}$ and $(V_B - V_A)$ is $90^\circ$. The input signal frequency is $10^x \, \mathrm{rad/sec}$, where ' x ' is ______

Solution

Given the input voltage, we have the following relationships: $$\theta + \theta = 90^\circ; \theta = 45^\circ$$ The tangent of the angle is given by: $$\tan \theta = \frac{X_C}{R}$$ Since $X_C = R$, it follows that: $$\frac{1}{W_C} = R$$ The work done $W$ is: $$W = \frac{1}{R_C} = \frac{10^{12}}{10^7} = 10^5$$

Question 48

Physics · Ray Optics and Optical Instruments · Numerical

A container contains a liquid with refractive index of $1.2$ up to a height of $60\,\mathrm{cm}$ and another liquid having refractive index $1.6$ is added to a height of $H$ above the first liquid. If viewed from above, the apparent shift in the position of the bottom of the container is $40\,\mathrm{cm}$. The value of $H$ is _____ $\mathrm{cm}$. (Consider liquids are immiscible.)

Answer: 80

Solution

Let $y$ be the apparent depth of the bottom. $$y = \frac{H}{1.6} + \frac{60}{1.2}$$ Shift $= 40$ $$H + 60 - y = 40$$ Substituting for $y$: $$H + 60 - \frac{H}{1.6} - \frac{60}{1.2} = 40$$ Simplifying: $$\frac{6}{16} H = 30$$ Solving for $H$: $$H = 80 \, cm$$

Question 49

Physics · Thermal Properties of Matter · Numerical

A wire of length 10 cm and diameter 0.5 mm is used in a bulb. The temperature of the wire is $1727^\circ C$ and power radiated by the wire is $94.2 \, \mathrm{W}$. Its emissivity is $\frac{x}{8}$ where $x$ = ________ (Given $\sigma = 6.0 \times 10^{-8} \, \mathrm{W} \, \mathrm{m}^{-2} \, \mathrm{K}^{-4}$, $\pi = 3.14$ and assume that the emissivity of wire material is same at all wavelength.)

Answer: 5

Solution

Given $L = 10 \, \mathrm{cm}$, $d = 0.5 \, \mathrm{mm}$, $T = 1727^\circ \mathrm{C} = 2000 \, \mathrm{K}$. Power, $P = 94.2 \, \mathrm{W}$. $P = \varepsilon \sigma A T^4$ $$94.2 = \varepsilon \times (6 \times 10^{-8}) (\pi d L) (2000)^4$$ $$94.2 = \varepsilon \times (6 \times 10^{-8}) (3.14)(0.5) (10^{-3}) (10 \times 10^{-2}) (2000)^4$$ $$\varepsilon = \frac{94.2}{(94.2)(16)} = \frac{5}{8}$$

Question 50

Physics · Thermodynamics · Numerical

An ideal gas has undergone through the cyclic process as shown in the figure. Work done by the gas in the entire cycle is _____ $\times 10^{-1}\,\mathrm{J}$. (Take $\pi = 3.14$)

Answer: 314

Solution

Area of circle, $W = \frac{\pi}{4} d_1 d_2$. $$W = \frac{\pi}{4} (500 - 300) \times 10^3 (350 - 150) \times 10^{-6}$$ $W = 31.4$ Joule $W = 314 \times 10^{-1}$ Joule

Chemistry

Question 51

Chemistry · Hydrocarbons · Single correct

Given below are two statements : Statement I : Ozonolysis followed by treatment with Zn, $H_2O$ of cis-2-butene gives ethanal. Statement II : The product obtained by ozonolysis followed by treatment with Zn, $H_2O$ of 3, 6-dimethyloct-4-ene has no chiral carbon atom. In the light of the above statements, choose the correct answer from the options given below

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

Answer: (c)

Solution

St.-I: Cis-2-butene is treated with (i) $\mathrm{O_3/Zn}$ and (ii) $\mathrm{H_2O}$ to form $2[\mathrm{CH_3-CHO}]$, which is ethanol. St.-II: The compound $\mathrm{H_3C-CH_2-CH-CH=CH-CH_2-CH_3}$ with $\mathrm{CH_3}$ groups is treated with (i) $\mathrm{O_3/Zn}$ and (ii) $\mathrm{H_2O}$ to form $2[\mathrm{CH_3-CH_2-CH-CO-CH_3}]$. The product has a chiral center. St-I: Correct statement St-II: Incorrect statement because product has chiral centre.

Question 52

Chemistry · Amines · Single correct

Which of the following amine (s) show (s) positive carbylamines test? Choose the correct answer from the options given below :

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

Answer: (c)

Solution

Only $1^\circ$ or primary amines gives positive carbylamines test. $$\mathrm{R{-}NH_2 \xrightarrow{CHCl_3 + KOH} R{-}N \equiv C}$$ (Alkyl iso cyanide, pungent) Option (A) and (C) are primary amine and give positive carbylamine test.

Question 53

Chemistry · Chemical Kinetics and Nuclear Chemistry · Single correct

Reaction $\mathrm{A(g) \rightarrow 2\, B(g) + C(g)}$ is a first order reaction. It was started with pure A \begin{tabular}{|c|c|} \hline \textbf{t/min} & \textbf{Pressure of system at time $t$/mm Hg} \\ \hline 10 & 160 \\ \hline $\infty$ & 240 \\ \hline \end{tabular} Which of the following option is incorrect?

  1. Initial pressure of A is 80 mm Hg
  2. The reaction never goes to completion
  3. Rate constant of the reaction is 1.693 min$^{-1}$
  4. Partial pressure of A after 10 minute is 40 mm Hg

Answer: (c)

Solution

The reaction is given as $\mathrm{A(g)} \rightarrow 2\, \mathrm{B(g)} + \mathrm{C(g)}$. At $t = 0$, the pressure is $P_0$. As $t \rightarrow \infty$, the pressures are $0$, $2P_0$, and $P_0$ respectively. The total pressure at infinity is $P_\infty = 3P_0 = 240$. Therefore, $P_0 = 80 \, \mathrm{mm \, of \, Hg}$. The equation for $Kt$ is $$Kt = \ln \left( \frac{P_\infty - P_0}{P_\infty - P_t} \right).$$ Substituting the values, we have $$K \times 10 = \ln \left( \frac{240 - 80}{240 - 160} \right).$$ Solving this gives $$K = \frac{\ln 2}{10} = 0.0693 \, \mathrm{min^{-1}}.$$ Therefore, option (3) is incorrect.

Question 54

Chemistry · Thermodynamics · Single correct

Total enthalpy change for freezing of 1 mol of water at $10^{\circ}C$ to ice at $-10^{\circ}C$ is ____ (Given : $\Delta_{fus} H = x \, kJ/mol$) $C_p \left[ H_2O(l) \right] = y \, Jmol^{-1} \, K^{-1}$ $C_p \left[ H_2O(s) \right] = z \, Jmol^{-1} \, K^{-1}$

  1. $-x - 10y - 10z$
  2. $-10(100x + y + z)$
  3. $10(100x + y + z)$
  4. $x - 10y - 10z$

Answer: (b)

Solution

The process involves the conversion of $\mathrm{H_2O_{(l)}}$ at $10^\circ \mathrm{C}$ to $\mathrm{H_2O_{(s)}}$ at $10^\circ \mathrm{C}$, and then to $\mathrm{H_2O_{(s)}}$ at $0^\circ \mathrm{C}$. The enthalpy change is calculated as follows: $$\Delta H = 1 \times y(0 - 10) - x \times 1000 + 1 \times z(-10^\circ - 0^\circ)$$ Simplifying, we have: $$\Delta H = -10(100x + y + z) Joule.$$

Question 55

Chemistry · Equilibrium · Single correct

An aqueous solution of HCl with pH 1.0 is diluted by adding equal volume of water (ignoring dissociation of water). The pH of HCl solution would (Given $\log 2 = 0.30$)

  1. reduce to 0.5
  2. increase to 1.3
  3. remain same
  4. increase to 2

Answer: (b)

Solution

HCl(aq) pH = 1; $[\mathrm{H}^+] = 10^{-1}$. If equal volume of water is added, concentration will become half. $$[\mathrm{H}^+]_{sol} = \frac{10^{-1}}{2}$$ pH = 1.3

Question 56

Chemistry · Alcohols, Phenols and Ethers · Single correct

Given below are two statements: Statement I: Dimethyl ether is completely soluble in water. However, diethyl ether is soluble in water to a very small extent. Statement II: Sodium metal can be used to dry diethyl ether and not ethyl alcohol. In the light of given statements, choose the correct answer from the options given below

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

Answer: (d)

Solution

St-I is correct because both given ether are soluble in water. Diethyl ether and butan-1-ol are miscible to almost the same extent, i.e., 7.5 and 9 gm per 100 ml water due to H-bonding. St-II is also correct because sodium metal is not used with ethyl alcohol as $\mathrm{H_2}$ gas is released with ethyl alcohol.

Question 57

Chemistry · Structure of Atom · Single correct

Which of the following statements are correct, if the threshold frequency of caesium is $5.16 \times 10^{14} \, \mathrm{Hz}$? A. When Cs is placed inside a vacuum chamber with an ammeter connected to it and yellow light is focused on Cs the ammeter shows the presence of current. B. When the brightness of the yellow light is dimmed, the value of the current in the ammeter is reduced. C. When a red light is used instead to the yellow light, the current produced is higher with respect to the yellow light. D. When a blue light is used, the ammeter shows the formation of current. E. When a white light is used, the ammeter shows formation of current. Choose the correct answer from the options given below:

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

Answer: (d)

Solution

Given $$\lambda = \frac{C}{\nu} = \frac{3 \times 10^8}{5.16 \times 10^{14}}$$ $$\lambda = 581.39 \, \mathrm{nm}$$ * $\lambda_{Photon}$ is near & below yellow light it can show photoelectric effect. * If intensity of light decreases photocurrent decreases. * Red light will not produce photoelectric effect. * $\nu_{Blue} > \nu_{yellow}$ so photoelectric current will be produced. * White light contain all frequencies so it will show photo electric current. Correct statements are A B D & E.

Question 58

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

Which of the following is the correct IUPAC name of given organic compound (X) ?

  1. 2-Bromo-2-methylbut-2-ene
  2. 3-Bromo-3-methylprop-2-ene
  3. 1-Bromo-2-methylbut-2-ene
  4. 4-Bromo-3-methylbut-2-ene

Answer: (c)

Solution

The compound shown is 1-Bromo-2-methyl but-2-ene.

Question 59

Chemistry · States of Matter · Single correct

At the sea level, the dry air mass percentage composition is given as nitrogen gas : 70.0, oxygen gas : 27.0 and argon gas : 3.0. If total pressure is 1.15 $\,$ $\mathrm{atm}$ , then calculate the ratio of followings respectively : (i) partial pressure of nitrogen gas to partial pressure of oxygen gas (ii) partial pressure of oxygen gas to partial pressure of argon gas (Given : Molar mass of N, O and Ar are 14, 16, and 40 $\,$ $\mathrm{g \, mol^{-1}}$ respectively)

  1. 4.26, 19.3
  2. 2.59, 11.85
  3. 5.46, 17.8
  4. 2.96, 11.2

Answer: (d)

Solution

Using Dalton's law of partial pressure, we have: $$\frac{P_{\mathrm{N_2}}}{P_{\mathrm{O_2}}} = \frac{x_{\mathrm{N_2}} \cdot P_T}{x_{\mathrm{O_2}} \cdot P_T} = \frac{n_{\mathrm{N_2}}}{n_{\mathrm{O_2}}}$$ Calculating the ratio: $$\frac{70/28}{27/32} = 2.96$$ For $P_{\mathrm{O_2}}$ and $P_{\mathrm{Ar}}$, we have: $$P_{\mathrm{O_2}} = n_{\mathrm{O_2}} = \frac{27/32}{3/40} = 11.25$$

Question 60

Chemistry · Electrochemistry · Single correct

Given below are two statements : Statement I : Mohr's salt is composed of only three types of ions-ferrous, ammonium and sulphate. Statement II : If the molar conductance at infinite dilution of ferrous, ammonium and sulphate ions are $x_1$, $x_2$ and $x_3$ S cm$^2$ mol$^{-1}$, respectively then the molar conductance for Mohr's salt solution at infinite dilution would be given by $x_1 + x_2 + 2x_3$ In the light of the given statements, choose the correct answer from the options given below :

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

Answer: (c)

Solution

Mohr's salt: $\mathrm{FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O}$ Using Kohlrausch law $$\lambda_m^\infty (Mohr's salt) = x_1 + 2x_2 + 2x_3$$

Question 61

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

The number of valence electrons present in the metal among Cr, Co, Fe and Ni which has the lowest enthalpy of atomisation is

  1. 8
  2. 9
  3. 6
  4. 10

Answer: (c)

Solution

Out of Cr, Co, Fe and Ni, chromium has the lowest heat of atomisation. $$Cr = [Ar] 3d^5 4s^1$$ Therefore, total six valence electrons in Cr.

Question 62

Chemistry · Analytical Chemistry · Single correct

When a salt is treated with sodium hydroxide solution it gives gas X. On passing gas X through reagent Y a brown coloured precipitate is formed. X and Y respectively, are

  1. $X = NH_3$ and $Y = HgO$
  2. $X = NH_3$ and $Y = K_2HgI_4 + KOH$
  3. $X = NH_4Cl$ and $Y = KOH$
  4. $X = HCl$ and $Y = NH_4Cl$

Answer: (b)

Solution

$NH_4^{+}+NaOH\xrightarrow{H_2O}NH_3\uparrow$

Question 63

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

The group 14 elements A and B have the first ionisation enthalpy values of 708 and 715 $\mathrm{kJ} \mathrm{mol}^{-1}$ respectively. The above values are lowest among their group members. The nature of their ions $\mathrm{A}^{2+}$ $\mathrm{B}^{4+}$ respectively is

  1. both reducing
  2. both oxidising
  3. reducing and oxidising
  4. oxidising and reducing

Answer: (c)

Solution

As per given information of ionisation energy, A = $\mathrm{Sn}$ $\&$ B = $\mathrm{Pb}$. $A^{+2}$ = $\mathrm{Sn}^{2+}$ = Reducing agent. $B^{+4}$ = $\mathrm{Pb}^{+4}$ = Oxidising agent.

Question 64

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

The first transition series metal ' M ' has the highest enthalpy of atomisation in its series. One of its aquated ion $\left( \mathrm{M}^{n+} \right)$ exists in green colour. The nature of the oxide formed by the above $\mathrm{M}^{n-}$ ion is:

  1. neutral
  2. acidic
  3. basic
  4. amphoteric

Answer: (c)

Solution

In 3d series, Vanadium has the highest enthalpy of atomization and the color of $\mathrm{V^{+3}}$ is green. Oxide formed by $\mathrm{V^{+3}}$ is $\mathrm{V_2O_3}$ (Basic oxide).

Question 65

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

Which of the following compounds is least likely to give effervescence of $CO_2$ in presence of aq. $NaHCO_3$ ?

Answer: (d)

Solution

Concept - Those compounds which are more acidic than $\mathrm{H_2CO_3}$ can give effervescence of $\mathrm{CO_2}$ with aqueous $\mathrm{NaHCO_3}$. Release $\mathrm{CO_2}$ gas with aqueous $\mathrm{NaHCO_3}$. $$[A.S.]_{Comp.} > [A.S.]_{\mathrm{H_2CO_3}}$$ Option 1, 2, and 3 give effervescence of $\mathrm{CO_2}$ gas with $\mathrm{NaHCO_3}$. Option (4) does not give $\mathrm{CO_2}$ gas with $\mathrm{NaHCO_3}$.

Question 66

Chemistry · Chemical Bonding and Molecular Structure · Single correct

Match the LIST-I with LIST-II. Choose the correct answer from the options given below : \begin{tabular}{|c|l|c|c|} \hline \multicolumn{2}{|c|}{LIST-I} & \multicolumn{2}{c|}{LIST-II} \\ \multicolumn{2}{|c|}{Molecule/ion} & \multicolumn{2}{c|}{Bond pair : lone pair} \\ \multicolumn{2}{|c|}{} & \multicolumn{2}{c|}{(on the central atom)} \\ \hline A. & ICl$_2^{-}$ & I. & 4 : 2 \\ \hline B. & H$_2$O & II. & 4 : 1 \\ \hline C. & SO$_2$ & III. & 2 : 3 \\ \hline D. & XeF$_4$ & IV. & 2 : 2 \\ \hline \end{tabular}

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

Answer: (b)

Solution

Question 67

Chemistry · Chemical Kinetics and Nuclear Chemistry · Single correct

A person's wound was exposed to some bacteria and then bacteria growth started to happen at the same place. The wound was later treated with some antibacterial medicine and the rate of bacterial decay (r) was found to be proportional with the square of the existing number of bacteria at any instance. Which of the following set of graphs correctly represents the 'before' and 'after' situation of the application of the medicine? [Given : $N =$ No. of bacteria, $t =$ time, bacterial growth follows 1$^{st}$ order kinetics.]

Answer: (b)

Solution

Before applying medicine $$\frac{dA}{dt} = K[A]$$ (First order growth) (Rate law) $$\frac{A}{A_0} = \frac{N}{N_0} = e^{Kt}$$ After applying medicine Active Bacteria $\rightarrow$ Inactive Bacteria $$r = -\frac{dA}{dt} = K[A]^2$$ (Rate law) $$y = Kx^2$$ Parabola

Question 68

Chemistry · Biomolecules · Single correct

Given below are two statements: Statement I : D-(+)-glucose + D-(+) fructose $\xrightarrow{-H_2O}$ Statement II : Invert sugar is formed during sucrose hydrolysis. In the light of the above statements, choose the correct answer from the options given below -

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

Answer: (b)

Solution

On hydrolysis of sucrose gives D-(+)-glucose and D-(-)-fructose while in St. (1) D-(+)-fructose is given evince. St-(1) is incorrect. St. II - It is correct because sucrose on hydrolysis gives invert sugar.

Question 69

Chemistry · Co-ordination Compounds · Single correct

An octahedral complex having molecular composition $Co. 5NH_3. Cl. SO_4$ has two isomers A and B. The solution of A gives a white precipitate with $AgNO_3$ solution and the solution of B gives white precipitate with $BaCl_2$ solution. The type of isomerism exhibited by the complex is,

  1. Co-ordinate isomerism
  2. Linkage isomerism
  3. Ionisation isomerism
  4. Geometrical isomerism

Answer: (c)

Solution

(A) complex is $[\mathrm{Co(NH_3)_5(SO_4)}] \mathrm{Cl}$ (3) (B) complex is $[\mathrm{Co(NH_3)_5Cl}] \mathrm{SO_4}$ Both (A) and (B) are Ionisation isomers.

Question 70

Chemistry · Haloalkanes and Haloarenes · Single correct

The reactions which cannot be applied to prepare an alkene by elimination, are

  1. B & E Only
  2. B, C & D Only
  3. A, C & D Only
  4. B & D Only

Answer: (d)

Solution

Option (B) and (D) reaction are not able to form alkene as a product.

Question 71

Chemistry · Some Basic Concepts of Chemistry · Numerical

An organic compound weighing $500\text{ mg}$ produced $220\text{ mg}$ of $\mathrm{CO_2}$ on complete combustion. The percentage composition of carbon in the compound is __________ $\%$ (nearest integer) [Given molar mass in $\text{g mol}^{-1}$ of $\mathrm{C}: 12$, $\mathrm{O}: 16$]

Answer: 12

Solution

Organic compound $\xrightarrow{CuO} CO_2 + H_2O$ $n_{CO_2} = \frac{220 \times 10^{-3}}{44} = 5 \times 10^{-3} moles$ $m_C = 5 \times 10^{-3} \times 12$ $\% m carbon = \frac{5 \times 10^{-3} \times 12}{500 \times 10^{-3}} \times 100 = 12\%$ Correct answer is 12

Question 72

Chemistry · Chemistry in Everyday Life · Numerical

Thyroxine, the hormone has given below structure. The percentage of iodine in thyroxine is _____ $\%$. (nearest integer) (Given molar mass in $\mathrm{g \, mol^{-1}}$ $\mathrm{C}$ : $12$, $\mathrm{H}$ : $1$, $\mathrm{O}$ : $16$, $\mathrm{N}$ : $14$, $\mathrm{I}$ : $127$)

Answer: 65

Solution

Molecular formula of Thyroxine $\Rightarrow \mathrm{C_{15}H_{11}O_4N_1I_4}$. Molecular mass of Thyroxine: C $\rightarrow 15 \times 12 = 180$ H $\rightarrow 11 \times 1 = 11$ O $\rightarrow 16 \times 4 = 64$ N $\rightarrow 14 \times 1 = 14$ I $\rightarrow 127 \times 4 = 508$ Molecular mass of Thyroxine $\Rightarrow 777$. Percentage of Iodine $= \frac{508}{777} \times 100 = 65.38\%$. Nearest integer $= 65$.

Question 73

Chemistry · Electrochemistry · Numerical

1 Faraday electricity was passed through $\mathrm{Cu}^{2+}(1.5 \, \mathrm{M}, 1 \, \mathrm{L})/\mathrm{Cu}$ and 0.1 Faraday was passed through $\mathrm{Ag}^+(0.2 \, \mathrm{M}, 1 \, \mathrm{L})/\mathrm{Ag}$ electrolytic cells. After this the two cells were connected as shown below to make an electrochemical cell. The emf of the cell thus formed at 298 K is-

Answer: 400

Solution

The reaction is $\mathrm{Cu^{+2} + 2e^- \rightarrow Cu}$. One faraday is the charge on 1 mole of electrons. Initially, at $t = 0$, there are 1.5 moles of $\mathrm{Cu^{+2}}$. At $t = t$, there is 1 mole, so 0.5 moles have reacted. The concentration of $\mathrm{Cu^{+2}}$ is 1M after electrolysis. The reaction for silver is $\mathrm{Ag^+ + e^- \rightarrow Ag}$. Initially, at $t = 0$, there are 0.2 moles of $\mathrm{Ag^+}$. At $t = t$, there are 0.1 moles remaining. The concentration of $\mathrm{Ag^+}$ is 0.1M after electrolysis. The cell reaction is $\mathrm{Cu_{(s)} + 2Ag^+_{(aq)} \rightarrow Cu^{+2}_{(aq)} + 2Ag_{(s)}}$. The Nernst equation is given by: $$E = E^\circ - \frac{0.06}{n} \log \left( \frac{[\mathrm{Cu^{+2}}]}{[\mathrm{Ag^+}]^2} \right)$$ Substituting the values: $$E = (0.8 - 0.34) - \frac{0.06}{2} \log \left( \frac{1}{(0.1)^2} \right) = 0.4 \, \mathrm{V}$$ The correct answer is 400mV.

Question 74

Chemistry · Solutions · Numerical

The percentage dissociation of a salt ($MX_3$) solution at given temperature (van't Hoff factor $i = 2$) is ______ $\%$ (Nearest integer)

Answer: 33

Solution

The reaction is given by $\($ $\mathrm{MX_3}$ $\rightarrow$ $\mathrm{M^{+3}}$ + 3$\mathrm{X^{\ominus}}$ $\)$. The formula for $\($ i $\)$ is $\($ i = 1 + (n - 1)$\alpha$ $\)$. Substituting the values, $\($ i = 1 + (4 - 1)$\alpha$ = 2 $\)$. Solving for $\($ $\alpha$ $\)$, we get $\($ $\alpha$ = $\frac{1}{3}$ = 33.33$\%$ $\approx$ 33$\%$ $\)$.

Question 75

Chemistry · Co-ordination Compounds · Numerical

The number of paramagnetic complex among $[\mathrm{FeF}_6]^{3-}$, $[\mathrm{Fe(CN)}_6]^{3-}$, $[\mathrm{Mn(CN)}_6]^{3-}$, $[\mathrm{Co(C_2O_4)}_3]^{3-}$, $[\mathrm{MnCl}_6]^{3-}$ and $[\mathrm{CoF}_6]^{3-}$, which involved $d^2sp^3$ hybridization is ____

Answer: 2

Solution

Q12. $[\mathrm{FeF}_6]^{3-}$ Paramagnetic $sp^3d^2$ $[\mathrm{Fe(CN)}_6]^{3-}$ Paramagnetic $d^2sp^3$ $[\mathrm{Mn(CN)}_6]^{3-}$ Paramagnetic $d^2sp^3$ $[\mathrm{Co(C_2O_4)}_3]^{3-}$ Diamagnetic $d^2sp^3$ $[\mathrm{MnCl}_6]^{3-}$ Paramagnetic $sp^3d^2$ $[\mathrm{CoF}_6]^{3-}$ Paramagnetic $sp^3d^2$ Only $[\mathrm{Fe(CN)}_6]^{3-}$ and $[\mathrm{Mn(CN)}_6]^{3-}$ are paramagnetic and $d^2sp^3$ hybridisation of metal.