JEE Main 29 July 2022 Shift 2 question paper with solutions

JEE Main 29 July 2022 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 · Complex Numbers and Quadratic Equations · Single correct

If $z \neq 0$ be a complex number such that $\left| z - \frac{1}{z} \right| = 2$, then the maximum value of $|z|$ is:

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

Answer: (d)

Solution

Given $|z - \frac{1}{z}| = 2$. Let $|z| = r$. We have: $$\left| z - \frac{1}{|z|} \right| \leq |z - \frac{1}{z}| \leq |z| + \frac{1}{|z|}$$ This implies: $$\left| r - \frac{1}{r} \right| \leq 2 \leq r + \frac{1}{r}$$ This is always true. Therefore: $$r - \frac{1}{r} \geq -2 and r - \frac{1}{r} \leq 2$$ Solving these inequalities: $$r^2 - 1 \leq 2r$$ $$r^2 - 2r \leq 1$$ $$(r - 1)^2 \leq 2$$ $$r - 1 \leq \sqrt{2}$$ Thus, $|z|_{\max} = 1 + \sqrt{2}$.

Question 2

Maths · Matrices · Single correct

Which of the following matrices can NOT be obtained from the matrix $$\begin{bmatrix} -1 & 2 \\ 1 & -1 \end{bmatrix}$$ by a single elementary row operation?

  1. $$\begin{bmatrix} 0 & 1 \\ 1 & -1 \end{bmatrix}$$
  2. $$\begin{bmatrix} 1 & -1 \\ -1 & 2 \end{bmatrix}$$
  3. $$\begin{bmatrix} -1 & 2 \\ -2 & 7 \end{bmatrix}$$
  4. $$\begin{bmatrix} -1 & 2 \\ -1 & 3 \end{bmatrix}$$

Answer: (c)

Solution

Given the matrix $$A = \begin{bmatrix} -1 & 2 \\ 1 & -1 \end{bmatrix}$$. (1) $R_1 \rightarrow R_1 + R_2$; $$\begin{bmatrix} 0 & 1 \\ 1 & -1 \end{bmatrix}$$ possible. (2) $R_1 \leftrightarrow R_2$; $$\begin{bmatrix} 1 & -1 \\ -1 & 2 \end{bmatrix}$$ possible. (3) Option is not possible. (4) $R_2 \rightarrow R_2 + 2R_1$; $$\begin{bmatrix} -1 & 2 \\ -1 & 3 \end{bmatrix}$$ possible.

Question 3

Maths · Determinants · Single correct

If the system of equations $x + y + z = 6$ $2x + 5y + \alpha z = \beta$ $x + 2y + 3z = 14$ has infinitely many solutions, then $\alpha + \beta$ is equal to :

  1. 8
  2. 36
  3. 44
  4. 48

Answer: (c)

Solution

Given the equations: $$x + y + z = 6 (1)$$ $$2x + 5y + \alpha z = \beta (2)$$ $$x + 2y + 3z = 14 (3)$$ From equation (1), we have $$x + y = 6 - z$$ From equation (3), we have $$x + 2y = 14 - 3z$$ On solving, $$x = z - 2 \implies y = 8 - 2z in (2)$$ Substitute in equation (2): $$2(z - 2) + 5(8 - 2z) + \alpha z = \beta$$ Simplifying, $$(\alpha - 8)z = \beta - 36$$ For having infinite solutions, $$\alpha - 8 = 0 \& \beta - 36 = 0$$ Thus, $$\alpha = 8, \beta = 36 (\alpha + \beta = 44)$$

Question 4

Maths · Continuity and Differentiability · Single correct

Let the function $$f(x) = \begin{cases} \frac{\log_e (1 + 5x) - \log_e (1 + \alpha x)}{x} & ; if x \neq 0 \\ 10 & ; if x = 0 \end{cases}$$ be continuous at $x = 0$. The $\alpha$ is equal to:

  1. 10
  2. -10
  3. 5
  4. -5

Answer: (d)

Solution

Given $$f(x) = \begin{cases} \frac{\ln(1+5x) - \ln(1+\alpha x)}{x} & ; x \neq 0 \\ 10 & ; x = 0 \end{cases}$$ We find $$\lim_{x \to 0} \frac{\ln(1+5x) - \ln(1+\alpha x)}{x} = 10$$ Using expansion, $$\lim_{x \to 0} \frac{(5x + \ldots) - (\alpha x + \ldots)}{x} = 10$$ This gives $$5 - \alpha = 10 \implies \alpha = -5$$

Question 5

Maths · Integrals · Single correct

If [t] denotes the greatest integer $\leq t$, then the value of $$\int_0^1 \left[ 2x - |3x^2 - 5x + 2| + 1 \right] \, dx$$ is:

  1. $\frac{\sqrt{37} + \sqrt{13} - 4}{6}$
  2. $\frac{\sqrt{37} - \sqrt{13} - 4}{6}$
  3. $\frac{-\sqrt{37} - \sqrt{13} + 4}{6}$
  4. $\frac{-\sqrt{37} + \sqrt{13} + 4}{6}$

Answer: (a)

Solution

Given $$I = \int_0^1 [2x - 13x^2 - 3x - 2x + 2 + 1] \, dx$$ Simplifying, we have $$I = \int_0^1 [2x - 1(3x - 2)(x - 1)] \, dx + \int_0^1 1 \, dx$$ Further simplifying, $$I = \int_0^{2/3} \left[ (2x - (3x^2 - 5x + 2)) \right] \, dx + \int_{2/3}^1 (2x + (3x^2 - 5x + 2)) \, dx + 1$$ Using the graph, we have $$\alpha = \frac{7 - \sqrt{37}}{6}, \beta = \frac{7 - \sqrt{13}}{6}$$ The integral becomes $$\int_0^\alpha (-2) \, dx + \int_\alpha^{1/3} (-1) \, dx + \int_{1/3}^\beta 0 \, dx + \int_\beta^{2/3} 1 \, dx$$ This simplifies to $$= -2\alpha - \left( \frac{1}{3} - \alpha \right) + \frac{2}{3} - \beta = -\alpha - \beta + \frac{1}{3}$$ For $$x \in \left( \frac{2}{3}, 1 \right)$$ We have $$3x^2 - 3x + 2 \in \left( \frac{4}{3}, 2 \right)$$ Thus, $$[3x^2 - 3x + 2] = 1$$ Therefore, $$\int_{2/3}^1 [3x^2 - 3x + 2] \, dx = 1 \left( 1 - \frac{2}{3} \right) = \frac{1}{3}$$ Hence, $$I = \left( \frac{1}{3} - (\alpha + \beta) \right) + \left( \frac{1}{3} \right) + 1$$ This simplifies to $$= \frac{5}{3} - \left( \frac{7 - \sqrt{37}}{6} + \frac{7 - \sqrt{13}}{6} \right)$$

Question 6

Maths · Sequences and Series · Single correct

Let $\{a_n\}_{n=0}^{\infty}$ be a sequence such that $a_0 = a_1 = 0$ and $$ a_{n+2} = 3a_{n+1} - 2a_{n+1}, \forall n \geq 0. $$ Then $a_{25} a_{23} - 2 a_{25} a_{22} - 2 a_{23} a_{24} + 4 a_{22} a_{24}$ is equal to:

  1. 483
  2. 528
  3. 575
  4. 624

Answer: (b)

Solution

Given $a_0 = 0$, $a_1 = 0$. $$a_{n+2} = 3 \, a_{n+1} - 2 \, a_n : n \geq 0$$ $$a_{n+2} - a_{n+1} = 2 \left( a_{n+1} - a_n \right) + 1$$ For $n = 0$, $a_2 - a_1 = 2 \left( a_1 - a_0 \right) + 1$. For $n = 1$, $a_3 - a_2 = 2 \left( a_2 - a_1 \right) + 1$. For $n = 2$, $a_4 - a_3 = 2 \left( a_3 - a_2 \right) + 1$. For $n = n$, $a_{n+2} - a_{n+1} = 2 \left( a_{n+1} - a_n \right) + 1$. $$(a_{n+2} - a_1) - 2 \left( a_{n+1} - a_0 \right) - (n + 1) = 0$$ $$a_{n+2} = 2 a_{n+1} + (n + 1)$$ Let $n \to n - 2$. $$a_n - 2 a_{n-1} = n - 1$$ Now $a_{25} a_{23} - 2 a_{25} a_{22} - 2 a_{23} a_{24} + 4 a_{22} a_{24}$ $$= (a_{25} - 2 a_{24}) (a_{23} - 2 a_{22}) = (24)(22) = 528$$

Question 7

Maths · Sequences and Series · Single correct

$$\sum_{r=1}^{20} (r^2 + 1)(r!)$$ is equal to:

  1. 22! - 21!
  2. 22! - 2 $\times$ (21!)
  3. 21! - 2 $\times$ (20!)
  4. 21! - 20!

Answer: (b)

Solution

Given the expression: $$\sum_{x=1}^{20} (r^2 + 1) r!$$ This can be rewritten as: $$\sum_{x=1}^{20} ((r+1)^2 - 2r) r!$$ Which simplifies to: $$\sum_{x=1}^{20} ((r+1)(r+1)! - r \cdot r!) - \sum_{r=1}^{20} r \cdot r!$$ Further simplifying gives: $$\sum_{x=1}^{20} ((r+1)(r+1)! - r \cdot r!) - \sum_{r=1}^{20} ((r+1)! - r!)$$ This results in: $$(21 \cdot 21! - 1) - (21! - 1)$$ Finally, we have: $$= 20 \cdot 21! = 22! - 2 \cdot 21!$$

Question 8

Maths · Integrals · Single correct

For $I(x) = \int \frac{\sec^2 x - 2022}{\sin^{2022} x} \, \mathrm{dx}$, if $I\left( \frac{\pi}{4} \right) = 2^{1011}$, then

  1. $3^{1010} I\left( \frac{\pi}{3} \right) - I\left( \frac{\pi}{6} \right) = 0$
  2. $3^{1010} I\left( \frac{\pi}{6} \right) - I\left( \frac{\pi}{3} \right) = 0$
  3. $3^{1011} I\left( \frac{\pi}{3} \right) - I\left( \frac{\pi}{6} \right) = 0$
  4. $3^{1011} I\left( \frac{\pi}{6} \right) - I\left( \frac{\pi}{3} \right) = 0$
Solution

$I(x)=\int \sec^2x\cdot\sin^{-2022}x\,dx$ Let $I=\sin^{-2022}x,\qquad II=\int \sec^2x\,dx=\tan x$ $= \tan x\cdot\sin^{-2022}x$ $-\int (2022)\tan x\, (\sin x)^{-2023}\cos x\,dx$ $=\tan x\cdot\sin^{-2022}x$ $-2022\int (\sin x)^{-2022}\,dx$ Hence, $I(x)=\tan x\cdot\sin^{-2022}x+C$ At $x=\dfrac{\pi}{4}$, $2^{1011} =\left(\dfrac1{\sqrt2}\right)^{-2022}+C$ $\therefore C=0$ Hence, $I(x)=\dfrac{\tan x}{(\sin x)^{2022}}$ $I\!\left(\dfrac{\pi}{6}\right) =\dfrac1{\sqrt3} \left(\dfrac12\right)^{-2022} =\dfrac{2^{2022}}{\sqrt3}$ $I\!\left(\dfrac{\pi}{3}\right) =\dfrac{\sqrt3} {\left(\dfrac{\sqrt3}{2}\right)^{2022}}$ $=\dfrac{2^{2022}} {(\sqrt3)^{2021}}$ $=\dfrac1{3^{1010}} \left(\dfrac{2^{2022}}{\sqrt3}\right)$ $\therefore 3^{1010}\,I\!\left(\dfrac{\pi}{3}\right) =I\!\left(\dfrac{\pi}{6}\right)$

Question 9

Maths · Differential Equations · Single correct

If the solution curve of the differential equation $\($ $\frac{dy}{dx}$ = $\frac{x+y-2}{x-y}$ $\)$ passes through the point $\($(2,1)$\)$ and $\($(k+1,2)$\)$, $\($k > 0$\)$, then

  1. $2 \tan^{-1}\left(\frac{1}{k}\right) = \log_e\left(k^2 + 1\right)$
  2. $\tan^{-1}\left(\frac{1}{k}\right) = \log_e\left(k^2 + 1\right)$
  3. $2 \tan^{-1}\left(\frac{1}{k+1}\right) = \log_e\left(k^2 + 2k + 2\right)$
  4. $2 \tan^{-1}\left(\frac{1}{k}\right) = \log_e\left(\frac{k^2 + 1}{k^2}\right)$

Answer: (a)

Solution

\[ \frac{dy}{dx} = \frac{x+y-2}{x-y} = \frac{(x-1)+(y-1)}{(x-1)-(y-1)} \] \[ x - 1 = X, \quad y - 1 = Y \] \[ \frac{dY}{dX} = \frac{X+Y}{X-Y} \] \[ Y = VX \qquad \frac{dY}{dX} = V + X\frac{dV}{dX} \] \[ V + X\frac{dV}{dX} = \frac{1+V}{1-V} \qquad X\frac{dV}{dX} = \frac{V^2+1}{1-V} \] \[ \int \frac{1-V}{1+V^2}\,dV = \int \frac{dX}{X} \] \[ \int \frac{dV}{1+V^2} - \frac{1}{2}\int \frac{2V\,dV}{1+V^2} = \int \frac{dX}{X} \] \[ \tan^{-1}V - \frac{1}{2}\ln\left(1+V^2\right) = \ln X + c \] \[ \tan^{-1}\left(\frac{Y}{X}\right) - \frac{1}{2}\ln\left(1+\frac{Y^2}{X^2}\right) = \ln(X) + c \] \[ \tan^{-1}\left(\frac{y-1}{x-1}\right) - \frac{1}{2}\ln\left(1+\frac{(y-1)^2}{(x-1)^2}\right) = \ln(x-1) + c \] Passes through $(2,1)$ \[ 0 - \frac{1}{2}\ln 1 = \ln 1 + c \quad \therefore c = 0 \] Passes through $(k+1, 2)$ \[ \therefore \tan^{-1}\left(\frac{1}{k}\right) - \frac{1}{2}\ln\left(1+\frac{1}{k^2}\right) = \ln k \] \[ \Rightarrow 2\tan^{-1}\left(\frac{1}{k}\right) = \log_e\left(k^2+1\right) \]

Question 10

Maths · Differential Equations · Single correct

Let $y = y (x)$ be the solution curve of the differential equation $\frac{dy}{dx} + \left( \frac{2x^2 + 11x + 13}{x^3 + 6x^2 + 11x + 6} \right)$ $y = \left( \frac{x+3}{x+1} \right), x > -1$, which passes through the point $(0,1)$. Then $y (1)$ is equal to:

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

Answer: (b)

Solution

Given $\($ $\frac{dy}{dx}$ + $\left$( $\frac{2x^2 + 11x + 13}{x^3 + 6x^2 + 11x + 6}$ $\right$) y = $\frac{x+3}{x+1}$ $\)$. $\($ $\int$ p(x) dx $\)$ I.F. = $\($ e^{$\int$ p(x) dx} $\)$ $\($ $\int$ p(x) dx = $\int$ $\left$( $\frac{2x^2 + 11x + 13}{(x+1)(x+2)(x+3)}$ $\right$) dx $\)$ Using partial fraction $\($ $\frac{2x^2 + 11x + 13}{(x+1)(x+2)(x+3)}$ = $\frac{A}{x+1}$ + $\frac{B}{x+2}$ + $\frac{C}{x+3}$ $\)$ $\($ A = $\frac{4}{2}$ = 2 $\)$ $\($ B = 1 $\)$ $\($ C = -1 $\)$ Therefore, $\($ $\int$ p(x) dx = A $\ln$(x+1) + B $\ln$(x+2) + C $\ln$(x+3) $\)$ $\($ = $\ln$ $\left$( $\frac{(x+1)^2(x+2)}{x+3}$ $\right$) $\)$ I.F. = $\($ e^{$\int$ p(x) dx} = $\frac{(x+1)^2(x+2)}{x+3}$ $\)$ Solution $\($ y(IF) = $\int$ Q(IF) dx $\)$ $\($ y $\left$( $\frac{(x+1)^2(x+2)}{x+3}$ $\right$) = $\int$ $\left$( $\frac{x+3}{x+1}$ $\right$) $\left$( $\frac{(x+1)^2(x+2)}{x+3}$ $\right$) dx $\)$ $\($ y $\left$( $\frac{(x+1)^2(x+2)}{x+3}$ $\right$) = $\frac{x^3}{3}$ + $\frac{3x^2}{2}$ + 2x + c $\)$ Passes through $\($ (0, 1) $\)$ $\($ C = $\frac{2}{3}$ $\)$ Now put $\($ x = 1 $\)$ $\($ $\Rightarrow$ y(1) = $\frac{3}{2}$ $\)$

Question 11

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

Let $m_1, m_2$ be the slopes of two adjacent sides of a square of side $a$ such that $a^2 + 11a + 3(m_2^2 + m_1^2) = 220$. If one vertex of the square is $(10(\cos \alpha - \sin \alpha), 10(\sin \alpha + \cos \alpha))$, where $\alpha \in \left(0, \frac{\pi}{2}\right)$ and the equation of one diagonal is $(\cos \alpha - \sin \alpha) x + (\sin \alpha + \cos \alpha) y = 10$, then $72(\sin^4 \alpha + \cos^4 \alpha) + a^2 - 3a + 13$ is equal to:

  1. 119
  2. 128
  3. 145
  4. 155

Answer: (b)

Solution

Given $m_1 m_2 = -1$. $$a^2 + 11a + 3 \left( m_1^2 + \frac{1}{m_1^2} \right) = 220$$ Equation of AC: $$AC = (\cos \alpha - \sin \alpha) + (\sin \alpha + \cos \alpha) \, y = 10$$ $$BD = (\sin \alpha - \cos \alpha) \, x + (\sin \alpha - \cos \alpha) \, y = 0$$ $$(10 \, (\cos \alpha - \sin \alpha), 10 \, (\sin \alpha - \cos \alpha))$$ Slope of AC: $$\left( \frac{\sin \alpha - \cos \alpha}{\sin \alpha + \cos \alpha} \right) = \tan \theta = M$$ Equation of line making an angle $\frac{\pi}{4}$ with AC: $$m_1, m_2 = \frac{m \pm \tan \frac{\pi}{4}}{1 \mp m \tan \frac{\pi}{4}}$$ $$= \frac{m + 1}{1 - m} or \frac{m - 1}{1 + m}$$ $$= \frac{\sin \alpha - \cos \alpha}{\sin \alpha + \cos \alpha}, \frac{\sin \alpha - \cos \alpha - 1}{\sin \alpha + \cos \alpha}$$ $$1 - \left( \frac{\sin \alpha - \cos \alpha}{\sin \alpha + \cos \alpha} \right), \frac{1 + \frac{\sin \alpha - \cos \alpha}{\sin \alpha + \cos \alpha}}{5(\cos \alpha + \sin \alpha)}$$ $$B \, (10(\cos \alpha - \sin \alpha), 10(\cos \alpha + \sin \alpha))$$ $$a = AB = \sqrt{2} \, BM = \sqrt{2} \, (5 \sqrt{2}) = 10$$ $$a = 10$$ Therefore, $$a^2 + 11a + 3 \left( m_1^2 + \frac{1}{m_1^2} \right) = 220$$ $$100 + 110 + 3 \left( \tan^2 \alpha + \cot^2 \alpha \right) = 220$$ Hence $\tan^2 \alpha = 3$, $\tan^2 \alpha = \frac{1}{3}$ $\implies \alpha = \frac{\pi}{3} or \frac{\pi}{6}$ Now $72 \left( \sin^4 \alpha + \cos^4 \alpha \right) + a^2 - 3a + 13$ $$= 72 \left( \frac{9}{16} + \frac{1}{16} \right) + 100 - 30 + 13$$ $$= 72 \left( \frac{5}{8} \right) + 83 = 45 + 83 = 128$$

Question 12

Maths · Trigonometric Functions · Single correct

The number of elements in the set $$S = \left\{ x \in \mathbb{R} : 2 \cos \left( \frac{x^2 + x}{6} \right) = 4^x + 4^{-x} \right\}$$ is:

  1. 1
  2. 3
  3. 0
  4. infinite

Answer: (a)

Solution

Given $$2 \cos \left( \frac{x^2 + x}{6} \right) = 4^x + 4^{-x}$$ L.H.S $\leq$ 2 and R.H.S $\geq$ 2. Hence L.H.S = 2 and R.H.S = 2. $$2 \cos \left( \frac{x^2 + x}{6} \right) = 2 4^x + 4^{-x} = 2$$ Check $x = 0$. Possible, hence only one solution.

Question 13

Maths · Properties of Triangles · Single correct

Let A ($\alpha$, $-2$), B ($\alpha$, 6) and C $\left( \frac{\alpha}{4}, -2 \right)$ be vertices of a $\triangle ABC$. If $\left( 5, \frac{\alpha}{4} \right)$ is the circumcentre of $\triangle ABC$, then which of the following is NOT correct about $\triangle ABC$:

  1. area is 24
  2. perimeter is 25
  3. circumradius is 5
  4. inradius is 2

Answer: (b)

Solution

$A(\alpha, -2)$, $B(\alpha, 6)$, $C\left(\dfrac{\alpha}{4}, -2\right)$ Since $AC$ is perpendicular to $AB$, $\triangle ABC$ is right angled at $A$. Circumcentre $=$ midpoint of $BC = \left(\dfrac{5\alpha}{8},\ 2\right)$ $$\therefore\ \frac{5\alpha}{8} = 5 \quad \text{and} \quad \frac{\alpha}{4} = 2$$ $\alpha = 8$ $$B = (8, 6)$$ $\text{Area} = \dfrac{1}{2}(6)(8) = 24$ $\text{Perimeter} = 24$ $\text{Circumradius} = 5$ $\text{Inradius} = \dfrac{\Delta}{s} = \dfrac{24}{12} = 2$

Question 14

Maths · Three Dimensional Geometry · Single correct

Let Q be the foot of perpendicular drawn from the point P (1, 2, 3) to the plane x + 2y + z = 14. If R is a point on the plane such that $\angle PRQ = 60^\circ$, then the area of $\triangle PQR$ is equal to:

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

Answer: (b)

Solution

Length of perpendicular $$PQ = \frac{|1 + 4 + 3 - 14|}{\sqrt{6}} = \sqrt{6}$$ $$QR = (PQ) \cot 60^\circ = \sqrt{2}$$ Therefore, the area of $\triangle PQR = \frac{1}{2} (PQ)(QR) = \sqrt{3}$

Question 15

Maths · Vector Algebra · Single correct

If $(2, 3, 9)$, $(5, 2, 1)$, $(1, \lambda, 8)$ and $(\lambda, 2, 3)$ are coplanar, then the product of all possible values of $\lambda$ is:

  1. $\frac{21}{2}$
  2. $\frac{59}{8}$
  3. $\frac{57}{8}$
  4. $\frac{95}{8}$

Answer: (d)

Solution

Given points A(2, 3, 9), B(5, 2, 1), C(1, $\lambda$, 8), and D($\lambda$, 2, 3). The condition is that the vectors $\overrightarrow{AB}$, $\overrightarrow{AC}$, and $\overrightarrow{AD}$ are coplanar, which implies: $$\begin{vmatrix} 3 & -1 & -8 \\ -1 & \lambda - 3 & -1 \\ \lambda - 2 & -1 & -6 \end{vmatrix} = 0$$ Expanding the determinant, we have: $$[-6(\lambda - 3) - 1] - 8(1 - (\lambda - 3)(\lambda - 2)) + (6 + (\lambda - 2)) = 0$$ Simplifying, we get: $$3(-6\lambda + 17) - 8(-\lambda^2 + 5\lambda - 5) + (\lambda + 4) = 8$$ This simplifies to: $$8\lambda^2 - 57\lambda + 95 = 0$$ The product of the roots is given by: $$\lambda_1 \lambda_2 = \frac{95}{8}$$

Question 16

Maths · Probability · Single correct

Bag I contains 3 red, 4 black and 3 white balls and Bag II contains 2 red, 5 black and 2 white balls. One ball is transferred from Bag I to Bag II and then a ball is draw from Bag II. The ball so drawn is found to be black in colour. Then the probability, that the transferred ball is red, is:

  1. $\frac{4}{9}$
  2. $\frac{5}{18}$
  3. $\frac{1}{6}$
  4. $\frac{3}{10}$

Answer: (b)

Solution

Given: A: Drown ball from boy II is black B: Red ball transferred The probability is given by: $$ \mathrm{P} \left( \frac{B}{A} \right) = \frac{\mathrm{P}(A \cap B)}{\mathrm{P}(A)} $$ Calculating: $$ = \frac{\frac{3}{9} \times \frac{5}{10}}{\frac{3}{9} \times \frac{5}{10} + \frac{4}{9} \times \frac{6}{10} + \frac{3}{9} \times \frac{5}{10}} $$ Simplifying: $$ = \frac{15}{15 + 24 + 15} = \frac{15}{54} = \frac{5}{18} $$

Question 17

Maths · Complex Numbers and Quadratic Equations · Single correct

Let $S = \{ z = x + iy : |z - 1 + i| \geq |z|, |z| < 2, |z + i| = |z - 1| \}$. Then the set of all values of $x$, for which $w = 2x + iy \in S$ for some $y \in \mathbb{R}$, is

  1. $\left( -\sqrt{2}, \frac{1}{2\sqrt{2}} \right]$
  2. $\left( -\frac{1}{\sqrt{2}}, \frac{1}{4} \right]$
  3. $\left( -\sqrt{2}, \frac{1}{2} \right]$
  4. $\left( \frac{-1}{\sqrt{2}}, \frac{1}{2\sqrt{2}} \right]$

Answer: (b)

Solution

Given $|z - 1 + i| \geq |z|$; $|z| < 2$; $|z + i| = |z - 1|$. Hence $w = 2x + iy \in S$. $2x \leq \frac{1}{2} \therefore x \leq \frac{1}{4}$. Now $$(2x)^2 + (2x)^2 < 4$$ $$x^2 < \frac{1}{2} \implies x \in \left( -\frac{1}{\sqrt{2}}, \frac{1}{\sqrt{2}} \right)$$ $$\therefore x \in \left( -\frac{1}{\sqrt{2}}, \frac{1}{4} \right]$$

Question 18

Maths · Vector Algebra · Single correct

Let $\vec{a}$, $\vec{b}$, $\vec{c}$ be three coplanar concurrent vectors such that angles between any two of them is same. If the product of their magnitudes is 14 and $$(\vec{a} \times \vec{b}) \cdot (\vec{b} \times \vec{c}) + (\vec{b} \times \vec{c}) \cdot (\vec{c} \times \vec{a}) + (\vec{c} \times \vec{a}) \cdot (\vec{a} \times \vec{b}) = 168$$ then $|\vec{a}| + |\vec{b}| + |\vec{c}|$ is equal to:

  1. 10
  2. 14
  3. 16
  4. 18

Answer: (c)

Solution

Given $|\vec{a} \parallel \vec{b} \parallel \vec{c}| = 14$. $\vec{a} \wedge \vec{b} = \vec{b} \wedge \vec{c} = \vec{c} \wedge \vec{a} = \theta = \frac{2\pi}{3}$. So, $\vec{a} \cdot \vec{b} = -\frac{1}{2} ab$, $\vec{b} \cdot \vec{c} = -\frac{1}{2} bc$, $\vec{a} \cdot \vec{c} = -\frac{1}{2} ac$. Let $(\vec{a} \times \vec{b}) \cdot (\vec{b} \times \vec{c}) = (\vec{a} \cdot \vec{b})(\vec{b} \cdot \vec{c}) - (\vec{a} \cdot \vec{c})(\vec{b} \cdot \vec{b})$. $$= \frac{1}{4} ab^2 c + \frac{1}{2} ab^2 c = \frac{3}{4} ab^2 c$$ Similarly, $$(\vec{b} \times \vec{c}) \cdot (\vec{c} \times \vec{a}) = \frac{3}{4} abc^2$$ $$(\vec{c} \times \vec{a}) \cdot (\vec{a} \times \vec{b}) = \frac{3}{4} a^2 bc$$ $$168 = \frac{3}{4} abc(a + b + c)$$ So, $(a + b + c) = 16$.

Question 19

Maths · Inverse Trigonometric Functions · Single correct

The domain of the function $$f(x) = \sin^{-1}\left(\frac{x^2 - 3x + 2}{x^2 + 2x + 7}\right)$$ is:

  1. $[1, \infty)$
  2. $(-1, 2]$
  3. $[-1, \infty)$
  4. $(-\infty, 2]$

Answer: (c)

Solution

Given $f(x) = \sin^{-1}\left( \frac{x^2 - 3x + 2}{x^2 + 2x + 7} \right)$. Domain $$\frac{x^2 - 3x + 2}{x^2 + 2x + 7} \geq -1 and \frac{x^2 - 3x + 2}{x^2 + 2x + 7} \leq 1$$ $$2x^2 - x + 9 \geq 0 and 5x - 5 \Rightarrow x \geq -1$$ $x \in \mathbb{R}$ Hence Domain $x \in [-1, \infty)$

Question 20

Maths · Mathematical Reasoning · Single correct

The statement $(p \Rightarrow q) \lor (p \Rightarrow r)$ is NOT equivalent to:

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

Answer: (b)

Solution

(p $\rightarrow$ q) $\lor$ (p $\rightarrow$ r) ($\sim$ p $\lor$ q) $\lor$ ($\sim$ p $\lor$ r) = $\sim$ p $\lor$ (q $\lor$ r) = p $\rightarrow$ (q $\lor$ r) $\equiv$ (3) is true. Now (1) (p $\land$ $\sim$ r) $\rightarrow$ q $\sim$ (p $\land$ $\sim$ r) $\lor$ q = ($\sim$ p $\lor$ r) $\lor$ q = $\sim$ p $\lor$ (r $\lor$ q) = p $\rightarrow$ (q $\lor$ r) (4) (p $\land$ $\sim$ q) $\rightarrow$ r = p $\rightarrow$ (q $\lor$ r)

Question 21

Maths · Probability · Numerical

The sum and product of the mean and variance of a binomial distribution are 82.5 and 1350 respectively. They the number of trials in the binomial distribution is:

Answer: 96

Solution

Let, mean = m = np and variance = v = npq, p + q = 1. Sum = m + v = $\frac{165}{2}$. Product = mv = 1350. On solving, m = np = 60 and v = npq = $\frac{45}{2}$. Therefore, q = $\frac{3}{8}$ and P = $\frac{5}{8}$. Hence n = 96.

Question 22

Maths · Complex Numbers and Quadratic Equations · Numerical

Let $\alpha$, $\beta$ ($\alpha > \beta$) be the roots of the quadratic equation $x^2 - x - 4 = 0$. If $P_n = \alpha^n - \beta^n$, $n \in \mathbb{N}$, then $$\frac{P_{15}P_{16} - P_{14}P_{16} - P_{15}^2 + P_{14}P_{15}}{P_{13}P_{14}}$$ is equal to .

Answer: 16

Solution

Given $P_n = \alpha^n - \beta^n$ and $x^2 - x - 4 = 0$. $$\frac{P_{15}P_{16} - P_{14}P_{16} - P_{15}^2 + P_{14}P_{15}}{P_{13}P_{14}} (1)$$ As $P_n - P_{n-1} = (\alpha^n - \beta^n) - (\alpha^{n-1} - \beta^{n-1})$ $$= \alpha^{n-2}(\alpha^2 - \alpha) - \beta^{n-2}(\beta^2 - \beta)$$ $$= 4(\alpha^{n-2} - \beta^{n-2})$$ $$P_n - P_{n-1} = 4 \, P_{n-2}$$ Hence Expression (1) $$\frac{P_{16}(P_{15} - P_{14}) - P_{15}(P_{15} - P_{14})}{P_{13}P_{14}}$$ $$= \frac{(P_{15} - P_{14})(P_{16} - P_{15})}{P_{13}P_{14}} = \frac{(4P_{13})(4P_{14})}{P_{13}P_{14}} = 16$$

Question 23

Maths · Matrices · Numerical

Let $x = \begin{bmatrix} 1 \\ 1 \\ 1 \end{bmatrix}$ and $A = \begin{bmatrix} -1 & 2 & 3 \\ 0 & 1 & 6 \\ 0 & 0 & -1 \end{bmatrix}$. For $k \in \mathbb{N}$, if $X' A^k X = 33$, then $k$ is equal to:

Answer: 10

Solution

Given the matrix equation: $\begin{bmatrix} 1&1&1 \end{bmatrix} \begin{bmatrix} -1&2&3\\ 0&1&6\\ 0&0&-1 \end{bmatrix} \begin{bmatrix} 1\\ 1\\ 1 \end{bmatrix} =33$ As $A^2$ $= \begin{bmatrix} -1&2&3\\ 0&1&6\\ 0&0&-1 \end{bmatrix} \begin{bmatrix} -1&2&3\\ 0&1&6\\ 0&0&-1 \end{bmatrix}$ $= \begin{bmatrix} 1&0&6\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ $A^4$ $=A^2A^2$ $= \begin{bmatrix} 1&0&6\\ 0&1&0\\ 0&0&1 \end{bmatrix} \begin{bmatrix} 1&0&6\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ $= \begin{bmatrix} 1&0&12\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ $A^8$ $=A^4A^4$ $= \begin{bmatrix} 1&0&12\\ 0&1&0\\ 0&0&1 \end{bmatrix} \begin{bmatrix} 1&0&12\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ $= \begin{bmatrix} 1&0&24\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ $A^{10}$ $=A^2A^8$ $= \begin{bmatrix} 1&0&6\\ 0&1&0\\ 0&0&1 \end{bmatrix} \begin{bmatrix} 1&0&24\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ $= \begin{bmatrix} 1&0&30\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ For $K$ Even $A^K= \begin{bmatrix} 1&0&3K\\ 0&1&0\\ 0&0&1 \end{bmatrix}$ $X^TA^KX=33$ (This is not correct) $\begin{bmatrix} 1&1&1 \end{bmatrix} \begin{bmatrix} 1&0&3K\\ 0&1&0\\ 0&0&1 \end{bmatrix} \begin{bmatrix} 1\\ 1\\ 1 \end{bmatrix}$ Therefore, $3K+3=33$ $\therefore\ K=10$ But it should be dropped as $33$ is not a matrix. If $K$ is odd $X^TA^KX=33$ $X^TAA^{K-1}X=33$ $\begin{bmatrix} 1&1&1 \end{bmatrix} \begin{bmatrix} -1&2&3\\ 0&1&6\\ 0&0&-1 \end{bmatrix} \begin{bmatrix} 1&0&3K-3\\ 0&1&0\\ 0&0&1 \end{bmatrix} \begin{bmatrix} 1\\ 1\\ 1 \end{bmatrix} =33$ $\begin{bmatrix} -1&3&8 \end{bmatrix} \begin{bmatrix} 3K-2\\ 1\\ 1 \end{bmatrix} =[33]$ $[-3K+13]=[33]$ $K=\dfrac{20}{3}$ (not possible)

Question 24

Maths · Permutations and Combinations · Numerical

The number of natural numbers lying between $1012$ and $23421$ that can be formed using the digits $2,3,4,5,6$ (repetition of digits is not allowed) and divisible by $55$ is ______.

Answer: 6

Solution

4 digit numbers For divisibility by 55, the number should be divisible by 5 and 11 both. Also, for divisibility by 11: $$a + c = b + 5$$ For $b = 1$: $a = 2$, $c = 4$ $a = 4$, $c = 2$ For $b = 2$: $a = 3$, $c = 4$ $a = 4$, $c = 3$ For $b = 3$: $a = 6$, $c = 2$ $a = 2$, $c = 6$ Therefore, 6 possible four digit numbers are divisible by 55. (II) 5 digit number is not possible. (Not possible)

Question 25

Maths · Binomial Theorem · Fill in the blank

If\[ \sum_{k=1}^{10} k^2\left({}^{10}C_k\right)^2=22000L, \] then $L$ is equal to \_\_\_\_.

Answer: 221

Solution

Given $$\sum_{K=1}^{10} K^2 \left( \binom{10}{K} \right)^2$$ This is equal to $$\sum_{K=1}^{10} \left( K \cdot \binom{10}{K} \right)^2 = \sum_{K=1}^{10} \left( 10 \cdot \binom{9}{K-1} \right)^2$$ This simplifies to $$= 100 \sum_{K=1}^{10} \binom{9}{K-1} \cdot \binom{9}{10-K}$$ Which is equal to $$= 100 \binom{18}{9} = 100 \left( \frac{18!}{9!9!} \right)$$ Thus, $$\Rightarrow 4862000 = 22000L$$ Hence, $$L = 221$$

Question 26

Maths · Continuity and Differentiability · Numerical

If [t] denotes the greatest integer $\leq t$, then number of points, at which the function $f(x) = 4 \lvert 2x + 3 \rvert + 9 \left[ x + \frac{1}{2} \right] - 12 \left[ x + 20 \right]$ is not differentiable in the open interval $(-20, 20)$, is ___.

Answer: 79

Solution

Given $f(x) = 4|2x + 3| + 9\left[x + \frac{1}{2}\right] - 12[x + 20]$. $x \in (-20, 20)$. $f(x)$ is not differentiable at $x = I \in \{-19, -18, \ldots, 0, \ldots, 19\} = 39$ points. At $x = I + \frac{1}{2}$, $f(x)$ is non-differentiable at 39 points. Check at $x = \frac{-3}{2}$. Discount at $x = \frac{-3}{2}$. Therefore, $N. R(1)$. Number of points of non-differentiability: $$= 39 + 39 + 1 = 79$$

Question 27

Maths · Applications of Derivatives · Numerical

If the tangent to the curve $y = x^3 - x^2 + x$ at the point $(a, b)$ is also tangent to the curve $y = 5x^2 + 2x - 25$ at the point $(2, -1)$, then $|2a + 9b|$ is equal to .

Answer: 195

Solution

Given $y = x^3 - x^2 + x$. At point $P(2, -1)$, the derivative $\frac{dy}{dx}$ is $22$. Therefore, the tangent to the curve at $P$ is given by: $$y + 1 = 22(x - 2)$$ Simplifying, we get: $$y = 22x - 45$$ For the curve $y = x^3 - x^2 + x$, the derivative is: $$\frac{dy}{dx} \bigg|_{C_2} = 3x^2 - 2x + 1$$ At point $Q(a, b)$, the derivative is: $$\frac{dy}{dx} \bigg|_Q = 3a^2 - 2a + 1$$ Setting this equal to $22$, we have: $$3a^2 - 2a + 1 = 22$$ Simplifying, we get: $$3a^2 - 2a - 21 = 0$$ Factoring, we find: $$3a^2 - 9a + 7a - 21 = 0$$ Solving, we find $a = 3$ and $b = 21$. The equation $2a + 9b = 195$ is satisfied. At $a = -7/3$, the tangent will be parallel, hence it is rejected.

Question 28

Maths · Conic Sections · Numerical

Let AB be a chord of length 12 of the circle $$(x - 2)^2 + (y + 1)^2 = \frac{169}{4}.$$ If tangents drawn to the circle at points A and B intersect at the point P, then five times the distance of point P from chord AB is equal to ___.

Answer: 72

Solution

Given the diagram, we have: $$\cos \theta = \frac{6}{\frac{13}{2}} = \frac{12}{13}$$ $$\sin \theta = \frac{5}{13}$$ The relation for PM is given by: $$\mathrm{PM} = \mathrm{AM} \cot \theta$$ Substituting the values, we get: $$\mathrm{PM} = 6 \left( \frac{12}{5} \right) \therefore 5(\mathrm{PM}) = 72$$

Question 29

Maths · Vector Algebra · Numerical

Let $\vec{a}$ and $\vec{b}$ be two vectors such that $|\vec{a} + \vec{b}|^2 = |\vec{a}|^2 + 2 |\vec{b}|^2$, $\vec{a} \cdot \vec{b} = 3$ and $|\vec{a} \times \vec{b}|^2 = 75$. Then $|\vec{a}|^2$ is equal to ____.

Answer: 14

Solution

Given $|\vec{a} + \vec{b}|^2 = |\vec{a}|^2 + 2|\vec{b}|^2$; $\vec{a} \cdot \vec{b} = 3$. As $|\vec{a}|^2 + |\vec{b}|^2 + 2 \vec{a} \cdot \vec{b} = |\vec{a}|^2 + 2|\vec{b}|^2$. $$|\vec{b}|^2 = 2 \vec{a} \cdot \vec{b} = 6$$ $$|\vec{a} \times \vec{b}|^2 = 75$$ $$|\vec{a}|^2 |\vec{b}|^2 - (\vec{a} \cdot \vec{b})^2 = 75$$ $$6 |\vec{a}|^2 - 9 = 75 \implies |\vec{a}|^2 = 14$$

Question 30

Maths · Conic Sections · Fill in the blank

Let $$S = \left\{ (x, y) \in \mathbb{N} \times \mathbb{N} : 9(x-3)^2 + 16(y-4)^2 \leq 144 \right\}$$ and $$T = \left\{ (x, y) \in \mathbb{R} \times \mathbb{R} : (x-7)^2 + (y-4)^2 \leq 36 \right\}.$$ The $n(S \cap T)$ is equal to ____.

Answer: 27

Solution

Given the set S: $\($ $\frac{(x-3)^2}{16}$ + $\frac{(y-4)^2}{9}$ $\leq$ 1 $\)$; $\($ x, y $\in$ $\{$1, 2, 3, $\ldots$$\}$ $\)$. Set T: $\($ (x-7)^2 + (y-4)^2 $\leq$ 36 $\)$; $\($ x, y $\in$ $\mathbb{R}$ $\)$. Let $\($ x-3 = x : y-4 = y $\)$. The set S: $\($ $\frac{x^2}{16}$ + $\frac{y^2}{9}$ $\leq$ 1 $\)$; $\($ x $\in$ $\{$-2, -1, 0, 1, $\ldots$$\}$ $\)$. The set T: $\($ (x-4)^2 + y^2 $\leq$ 36 $\)$; $\($ y $\in$ $\{$-3, -2, -1, 0, $\ldots$$\}$ $\)$. The intersection $\($ S $\cap$ T = (-2, 0), (-1, 0), $\ldots$, (4, 0) $\rightarrow$ (7) $\)$. $\($(-1, 1), (0, 1), $\ldots$, (3, 1) $\rightarrow$ (5) $\)$. $\($(-1, -1), (0, -1), $\ldots$, (3, -1) $\rightarrow$ (5) $\)$. $\($(-1, 2), (0, 2), (1, 2), (2, 2) $\rightarrow$ (4) $\)$. $\($(-1, -2), (0, -2), (1, -2), (2, -2) $\rightarrow$ (4) $\)$. $\($(0, 3) (0, -3) $\rightarrow$ (2) $\)$.

Physics

Question 31

Physics · Electric Charges and Fields · Single correct

Two identical metallic spheres A and B when placed at certain distance in air repel each other with a force of F. Another identical uncharged sphere C is first placed in contact with A and then in contact with B and finally placed at midpoint between spheres A and B. The force experienced by sphere C will be:

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

Answer: (b)

Solution

Let $q_A = q_B = q$. $$F = \frac{Kq^2}{r^2}$$ When C is placed in contact with A, charge on A and C will be $\frac{q}{2}$. Now C is placed in contact with B, charge on B and C will be $\frac{q + \frac{q}{2}}{2} = \frac{3q}{4}$. Now, $$\frac{q}{2} \overset{F_1}{\longleftarrow} A \overset{F_2}{\longrightarrow} C \overset{F_2}{\longrightarrow} B \frac{3q}{4}$$ $$F' = F_2 - F_1 = \left( \frac{K \frac{3q}{4} - K \frac{q}{2}}{\frac{r^2}{4}} \right) \cdot \frac{3q}{4}$$ $$= \frac{3Kq^2}{4r^2} = \frac{3F}{4} (B)$$

Question 32

Physics · Physical World, Units and Measurements · Single correct

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

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

Answer: (b)

Solution

Torque is given by $Torque = F \times r_\perp$ and is measured in Nm. Stress is given by $Stress = \frac{Force}{Area}$ and is measured in N/m$^2$. Latent heat is given by $Latent heat = \frac{Energy}{Mass}$ and is measured in J Kg$^{-1}$. Power is given by $Power = \frac{Work}{Time}$ and is measured in N ms$^{-1}$. The correct matching is A-III, B-IV, C-II, D-I.

Question 33

Physics · Electrostatic Potential and Capacitance · Single correct

Two identical thin metal plates has charge $q_1$ and $q_2$ respectively such that $q_1 > q_2$. The plates were brought close to each other to form a parallel plate capacitor of capacitance $C$. The potential difference between them is :

  1. $\frac{(q_1 + q_2)}{C}$
  2. $\frac{(q_1 - q_2)}{C}$
  3. $\frac{(q_1 - q_2)}{2C}$
  4. $\frac{2(q_1 - q_2)}{C}$

Answer: (c)

Solution

Electric field between plates is given by $E = \frac{q_1 - q_2}{2A \epsilon_0}$. The potential $V$ is given by $V = Ed = \frac{q_1 - q_2}{2A \epsilon_0} d$. Thus, $V = \frac{q_1 - q_2}{2C}$.

Question 34

Physics · Current Electricity · Single correct

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Alloys such as constantan and manganin are used in making standard resistance coils. Reason R: Constantan and manganin have very small value of temperature coefficient of resistance. In the light of the above statements, choose the correct answer from the options given below.

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

Answer: (a)

Solution

Theory based

Question 35

Physics · Current Electricity · Single correct

A 1 m long wire is broken into two unequal parts X and Y. The X part of the wire is stretched into another wire W. Length of W is twice the length of X and the resistance of W is twice that of Y. Find the ratio of length of X and Y.

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

Answer: (b)

Solution

Given $\($ $\frac{R_X}{R_Y}$ = $\frac{\ell_X}{\ell_Y}$ $\)$. When wire is stretched to double of its length, then resistance becomes 4 times. $\($ R_W = 4R_X = 2R_Y $\)$. $\($ $\frac{R_X}{R_Y}$ = $\frac{1}{2}$ $\)$. So, $\($ $\frac{\ell_X}{\ell_Y}$ = $\frac{1}{2}$ $\)$.

Question 36

Physics · Moving Charges and Magnetism · Single correct

A wire X of length 50 cm carrying a current of 2 A is placed parallel to a long wire Y of length 5 m. The wire Y carries a current of 3 A. The distance between two wires is 5 cm and currents flow in the same direction. The force acting on the wire Y is :

  1. $1.2 \times 10^{-5}\,\mathrm{N}$ directed towards wire X.
  2. $1.2 \times 10^{-4}\,\mathrm{N}$ directed away from wire X.
  3. $1.2 \times 10^{-4}\,\mathrm{N}$ directed towards wire X.
  4. $2.4 \times 10^{-5}\,\mathrm{N}$ directed towards wire X.

Answer: (a)

Solution

Force of interaction = $I_1 \, \ell_1 \, B_{12}$ $$= \frac{\mu_0 I_1 I_2}{2 \pi r} \ell_1$$ $$= \frac{4 \pi \times 10^{-7} \times 6 \times 0.5}{2 \pi \times 5 \times 10^{-2}}$$ $$= 1.2 \times 10^{-5} towards X$$

Question 37

Physics · Motion in a Straight Line · Single correct

A juggler throws balls vertically upwards with same initial velocity in air. When the first ball reaches its highest position, he throws the next ball. Assuming the juggler throws n balls per second, the maximum height the balls can reach is

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

Answer: (d)

Solution

Time taken by ball to reach highest point is $\frac{u}{g}$. Frequency of throw is $\frac{g}{u} = n$. Therefore, $u = \frac{g}{n}$. The maximum height $H_{max}$ is given by $$H_{max} = \frac{u^2}{2g} = \frac{\left(\frac{g}{n}\right)^2}{2g}$$ which simplifies to $$\frac{g}{2n^2}.$$

Question 38

Physics · Alternating Current · Single correct

A circuit element X when connected to an a.c. supply of peak voltage 100 V gives a peak current of 5 A which is in phase with the voltage. A second element Y when connected to the same a.c. supply also gives the same value of peak current which lags behind the voltage by $\frac{\pi}{2}$. If X and Y are connected in series to the same supply, what will be the rms value of the current in ampere?

  1. $\frac{10}{\sqrt{2}}$
  2. $\frac{5}{\sqrt{2}}$
  3. $5\sqrt{2}$
  4. $\frac{5}{2}$

Answer: (d)

Solution

Element X should be resistive with $R = 20 \, \Omega$. Element Y should be inductive with $X_L = 20 \, \Omega$. When X and Y are connected in series, $$Z = \sqrt{X_L^2 + R^2} = 20 \sqrt{2}$$ $$I_0 = \frac{E_0}{Z} = \frac{100}{20 \sqrt{2}} = \frac{5}{\sqrt{2}} \, \mathrm{A}$$ $$I_{\mathrm{rms}} = \frac{I_0}{\sqrt{2}} = \frac{5}{2} \, \mathrm{A}$$

Question 39

Physics · Wave Optics · Single correct

An unpolarised light beam of intensity $2I_0$ is passed through a polaroid P and then through another polaroid Q which is oriented in such a way that its passing axis makes an angle of $30^\circ$ relative to that of P. The intensity of the emergent light is

  1. $\frac{I_0}{4}$
  2. $\frac{I_0}{2}$
  3. $\frac{3I_0}{4}$
  4. $\frac{3I_0}{2}$

Answer: (c)

Solution

Given $I_1 = \frac{1}{2}(2I_0) = I_0$. $I_2 = I_1 \cos^2 30^\circ$. Therefore, $I_2 = I_0 \cdot \frac{3}{4} = \frac{3I_0}{4}$.

Question 40

Physics · Dual Nature of Radiation and Matter · Single correct

An $\alpha$ particle and a proton are accelerated from rest through the same potential difference. The ratio of linear momenta acquired by above two particles will be:

  1. $\sqrt{2} : 1$
  2. $2\sqrt{2} : 1$
  3. $4\sqrt{2} : 1$
  4. 8 : 1

Answer: (b)

Solution

Given $p = \sqrt{2mE} = \sqrt{2mqV}$. The ratio $\frac{p_\alpha}{p_p}$ is given by $$\frac{p_\alpha}{p_p} = \sqrt{\frac{m_\alpha q_\alpha}{m_p q_p}} = \sqrt{\frac{4}{1} \times \frac{2}{1}}$$ This simplifies to $$= \frac{2\sqrt{2}}{1}$$

Question 41

Physics · Atoms · Single correct

Read the following statements: (A) Volume of the nucleus is directly proportional to the mass number. (B) Volume of the nucleus is independent of mass number. (C) Density of the nucleus is directly proportional to the mass number. (D) Density of the nucleus is directly proportional to the cube root of the mass number. (E) Density of the nucleus is independent of the mass number. Choose the correct option from the following options.

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

Answer: (b)

Solution

Given $R \propto A^{1/3}$. $$V = \frac{4}{3} \pi R^3 \propto A$$ Mass $\propto A$. So density is independent of $A$.

Question 42

Physics · Gravitation · Single correct

An object of mass 1 kg is taken to a height from the surface of earth which is equal to three times the radius of earth. The gain in potential energy of the object will be [If, $g=10 \, \mathrm{m/s^2}$ and radius of earth $= 6400 \, \mathrm{km}$]

  1. 48 MJ
  2. 24 MJ
  3. 36 MJ
  4. 12 MJ

Answer: (a)

Solution

The initial potential energy is given by $$U_i = -\frac{GMm}{R}$$ The final potential energy is $$U_f = -\frac{GMm}{4R}$$ The change in potential energy is $$\Delta U = U_f - U_i = \frac{3GMm}{4R}$$ This is equal to $$= \frac{3}{4} mgR$$ Substituting the values, $$= \frac{3}{4} \times 1 \times 10 \times 64 \times 10^5$$ This results in $$= 48 \, MJ$$

Question 43

Physics · Motion in a Straight Line · Single correct

A ball is released from a height $h$. If $t_1$ and $t_2$ be the time required to complete first half and second half of the distance respectively. Then, choose the correct relation between $t_1$ and $t_2$.

  1. $t_1 = (\sqrt{2}) t_2$
  2. $t_1 = (\sqrt{2} - 1) t_2$
  3. $t_2 = (\sqrt{2} + 1) t_1$
  4. $t_2 = (\sqrt{2} - 1) t_1$

Answer: (d)

Solution

For first $\frac{h}{2}$ $$\frac{h}{2} = \frac{1}{2} g t_1^2$$ For total height $h$ $$h = \frac{1}{2} g (t_1 + t_2)^2$$ $$\frac{1}{\sqrt{2}} = \frac{t_1}{t_1 + t_2}$$ $$1 + \frac{t_2}{t_1} = \sqrt{2}$$ $$\frac{t_1}{t_2} = \frac{1}{\sqrt{2} - 1}$$

Question 44

Physics · Laws of Motion · Single correct

Two bodies of masses $m_1 = 5 \, \mathrm{kg}$ and $m_2 = 3 \, \mathrm{kg}$ are connected by a light string going over a smooth light pulley on a smooth inclined plane as shown in the figure. The system is at rest. The force exerted by the inclined plane on the body of mass $m_1$ will be :[Take $g = 10 \, \mathrm{ms^{-2}}$]

  1. 30 N
  2. 40 N
  3. 50 N
  4. 60 N

Answer: (b)

Solution

For equilibrium $m_2 g = m_1 g \sin \theta$. $$\sin \theta = \frac{m_2}{m_1} = \frac{3}{5}$$ $$\cos \theta = \frac{4}{5}$$ Normal force on $m_1 = 5g \cos \theta$ $$= 5 \times 10 \times \frac{4}{5} = 40 \, \mathrm{N}$$

Question 45

Physics · Work, Energy and Power · Single correct

If momentum of a body is increased by 20$\%$, then its kinetic energy increases by:

  1. 36$\%$
  2. 40$\%$
  3. 44$\%$
  4. 48$\%$

Answer: (c)

Solution

P' = P + $\frac{20}{100}$ P = 1.2 P $\%$ change in KE = $\frac{K' - K}{K}$ $\times$ 100 = $\left$( $\frac{\frac{P'^2}{2m} - \frac{P^2}{2m}}{\frac{P^2}{2m}}$ $\right$) $\times$ 100 = [(1.2)^2 - 1] $\times$ 100 = 44 $\%$

Question 46

Physics · System of Particles and Rotational Motion · Single correct

The torque of a force $5\hat{i} + 3\hat{j} - 7\hat{k}$ about the origin is $\tau$. If the force acts on a particle whose position vector is $2\hat{i} + 2\hat{j} + \hat{k}$, then the value of $\tau$ will be:

  1. $11\hat{i} + 19\hat{j} - 4\hat{k}$
  2. $-11\hat{i} + 9\hat{j} - 16\hat{k}$
  3. $-17\hat{i} + 19\hat{j} - 4\hat{k}$
  4. $7\hat{i} + 9\hat{j} + 16\hat{k}$

Answer: (c)

Solution

Given $\vec{\tau} = \vec{r} \times \vec{F} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 2 & 2 & 1 \\ 5 & 3 & -7 \end{vmatrix}$. This expands to $= \hat{i}(2(-7) - 1 \cdot 3) - \hat{j}(2(-7) - 1 \cdot 5) + \hat{k}(2 \cdot 3 - 2 \cdot 5)$. Simplifying, we get $= \hat{i}(-14 - 3) - \hat{j}(-14 - 5) + \hat{k}(6 - 10)$. Thus, $\vec{\tau} = -17\hat{i} + 19\hat{j} - 4\hat{k}$.

Question 47

Physics · Thermodynamics · Single correct

A thermodynamic system is taken from an original state D to an intermediate state E by the linear process shown in the figure. Its volume is then reduced to the original volume from E to F by an isobaric process. The total work done by the gas from D to E to F will be

  1. -450 \, $\mathrm{J}$
  2. 450 \, $\mathrm{J}$
  3. 900 \, $\mathrm{J}$
  4. 1350 \, $\mathrm{J}$

Answer: (b)

Solution

Question 48

Physics · Magnetism and Matter · Single correct

The vertical component of the earth's magnetic field is $6 \times 10^{-5} \, \mathrm{T}$ at any place where the angle of dip is $37^\circ$. The earth's resultant magnetic field at that place will be (Given $\tan 37^\circ = \frac{3}{4}$)

  1. $8 \times 10^{-5} \, \mathrm{T}$
  2. $6 \times 10^{-5} \, \mathrm{T}$
  3. $5 \times 10^{-4} \, \mathrm{T}$
  4. $1 \times 10^{-4} \, \mathrm{T}$

Answer: (d)

Solution

Given $\delta = 37^\circ$. The vertical component $B_V = B \sin \delta$. $$6 \times 10^{-5} = B \frac{3}{5}$$ Solving for $B$, we have: $$B = 10 \times 10^{-5} \, \mathrm{T}$$ Thus, $B = 10^{-4} \, \mathrm{T}$.

Question 49

Physics · Kinetic Theory · Single correct

The root mean square speed of smoke particles of mass $5 \times 10^{-17} \, \mathrm{kg}$ in their Brownian motion in air at NTP is approximately. [Given $k = 1.38 \times 10^{-23} \, \mathrm{JK}^{-1}$]

  1. 60 mm s$^{-1}$
  2. 12 mm s$^{-1}$
  3. 15 mm s$^{-1}$
  4. 36 mm s$^{-1}$

Answer: (c)

Solution

The root mean square velocity $V_{rms}$ is given by the equation: $$V_{rms} = \sqrt{\frac{3kT}{m}} = \sqrt{\frac{3 \times 1.38 \times 10^{-23} \times 293}{5 \times 10^{-17}}}$$ This is approximately equal to $15 \, mm/s$.

Question 50

Physics · Ray Optics and Optical Instruments · Single correct

Light enters from air into a given medium at an angle of $45^\circ$ with interface of the air-medium surface. After refraction, the light ray is deviated through an angle of $15^\circ$ from its original direction. The refractive index of the medium is :

  1. 1.732
  2. 1.333
  3. 1.414
  4. 2.732

Answer: (c)

Solution

Given $i = 45^\circ$. The deviation $D = i - r$. So, $15^\circ = 45 - r \Rightarrow r = 30^\circ$. Using Snell's law, $n_1 \sin i = n_2 \sin r$. Therefore, $1 \cdot \sin 45^\circ = \mu \cdot \sin 30^\circ$. This gives $\frac{1}{\sqrt{2}} = \mu \cdot \frac{1}{2}$. Solving for $\mu$, we get $\mu = \sqrt{2} = 1.414$.

Question 51

Physics · Laws of Motion · Numerical

A tube of length 50 cm is filled completely with an incompressible liquid of mass 250 g and closed at both ends. The tube is then rotated in horizontal plane about one of its ends with a uniform angular velocity $x \sqrt{F}$ rad s$^{-1}$. If $F$ be the force exerted by the liquid at the other end then the value of $x$ will be _____.

Answer: 4

Solution

The force is given by the integral of the differential mass times the square of the angular velocity times the distance. $$F = \int (dm) \omega^2 x$$ Substituting the limits from 0 to $L$, we have: $$= \frac{m}{L} \omega^2 \frac{L^2}{2}$$ Simplifying, $$= \frac{m \omega^2 L}{2}$$ Solving for $\omega$, $$\omega = \sqrt{\frac{2}{mL}} \sqrt{F}$$ Substituting the given values, $$= \sqrt{\frac{2}{0.25 \times 0.5}} \sqrt{F}$$ Simplifying further, $$= \sqrt{16} \sqrt{F}$$ Finally, $$= 4 \sqrt{F}$$

Question 52

Physics · Electromagnetic Waves · Numerical

Nearly 10$\%$ of the power of a 110 \, $\mathrm{W}$ light bulb is converted to visible radiation. The change in average intensities of visible radiation, at a distance of 1 m from the bulb to a distance of 5 m is $a \times 10^{-2} \, \mathrm{W/m^2}$. The value of 'a' will be

Answer: 84

Solution

Given $P' = 10\%$ of $110 \, \mathrm{W}$. $$= \frac{10}{100} \times 110 \, \mathrm{W}$$ $$= 11 \, \mathrm{W}$$ $I_1 - I_2 = \frac{P'}{4 \pi r_1^2} - \frac{P'}{4 \pi r_2^2}$ $$= \frac{11}{4 \pi} \left[ \frac{1}{1} - \frac{1}{25} \right]$$ $$= \frac{11}{4 \pi} \times \frac{24}{25}$$ $$= \frac{264}{\pi} \times 10^{-2} = 84 \times 10^{-2} \, \mathrm{W/m^2}$$

Question 53

Physics · Mechanical Properties of Solids · Numerical

A metal wire of length 0.5 m and cross-sectional area $10^{-4} \, \mathrm{m}^2$ has breaking stress $5 \times 10^8 \, \mathrm{Nm}^{-2}$. A block of 10 kg is attached at one end of the string and is rotating in a horizontal circle. The maximum linear velocity of block will be ____ $\mathrm{ms}^{-1}$.

Answer: 50

Solution

Given $T = \frac{mv^2}{\ell} = \frac{10 \times v^2}{0.5} = 20v^2$. $T_{max} = Breaking stress \times Area$ $= 5 \times 10^8 \times 10^{-4} = 5 \times 10^4$. $20V^2 = 5 \times 10^4$ $V = \sqrt{\frac{1}{4} \times 10^4} = 50 \, \mathrm{m/s}$

Question 54

Physics · Mechanical Properties of Fluids · Numerical

The velocity of a small ball of mass 0.3 g and density 8 g/cc when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is 1.3 g/cc, then the value of viscous force acting on the ball will be $x \times 10^{-4} \, \mathrm{N}$, the value of $x$ is ____. [use $g = 10 \, \mathrm{m/s^2}$]

Answer: 25

Solution

Given $F_V + F_B = mg$ (v = constant). $F_V = mg - F_B$ $= \rho_B V g - \rho_L V g$ $= (\rho_B - \rho_L) V g$ $= (8 - 1.3) \times 10^3 \times \frac{0.3 \times 10^{-3}}{8 \times 10^3} \times 10$ $= \frac{6.7 \times 0.3}{8} \times 10^{-2}$ (g = 10) $= \frac{67 \times 3}{8} \times 10^{-4} = 25.125 \times 10^{-4}$ Ans. 25.125

Question 55

Physics · Communication Systems · Numerical

A modulating signal $2\sin(6.28 \times 10^6 t)$ is added to the carrier signal $4\sin (12.56 \times 10^9 t)$ for amplitude modulation. The combined signal is passed through a non-linear square law device. The output is then passed through a band pass filter. The bandwidth of the output signal of band pass filter will be___MHz.

Answer: 2

Solution

Frequencies present in output of square law device $2f_c$, $f_c + f_m$, $f_c$, $f_c - f_m$, $2f_m$, $f_m$. After passing through band bass filter: $f_c + f_m$, $f_c$, $f_c - f_m$. Band width $= 2f_m$ $$= \frac{2\omega_m}{2\pi} = \frac{6.28 \times 10^6}{3.14}$$ $$= 2 \, MHz$$

Question 56

Physics · Mechanical Properties of Solids · Numerical

The speed of a transverse wave passing through a string of length 50 cm and mass 10 g is 60 ms$^{-1}$. The area of cross-section of the wire is 2.0 mm$^2$ and its Young's modulus is $1.2 \times 10^{11}$ Nm$^{-2}$. The extension of the wire over its natural length due to its tension will be $x \times 10^{-5}$ m. The value of $x$ is ______.

Answer: 15

Solution

Given $V_w = \sqrt{\frac{T}{\mu}}$. $$60 = \sqrt{\frac{T}{10 \times 10^{-3}}} \times 0.5$$ $$T = \frac{(60)^2 \times 10^{-2}}{0.5} = 72 \, \mathrm{N}$$ $$\Delta \ell = \frac{F \ell}{AY} = \frac{72 \times 0.5}{2 \times 10^{-6} \times 1.2 \times 10^{11}}$$ $$= \frac{72 \times 5}{24} \times 10^{-5} = 15 \times 10^{-5}$$ Ans. 15

Question 57

Physics · Oscillations · Numerical

The metallic bob of simple pendulum has the relative density 5. The time period of this pendulum is 10 s. If the metallic bob is immersed in water, then the new time period becomes $5\sqrt{x}$ s. The value of $x$ will be _______.

Answer: 5

Solution

The equation for the effective weight is given by: $$mg' = mg - F_B$$ where $F_B$ is the buoyant force. Therefore, the effective acceleration $g'$ is: $$g' = \frac{mg - F_B}{m}$$ Substituting the expression for the buoyant force, we have: $$g' = \frac{\rho_B V g - \rho_w V g}{\rho_B V}$$ Simplifying, we get: $$g' = \left( \frac{\rho_B - \rho_w}{\rho_B} \right) g$$ Substituting the given values: $$g' = \frac{5 - 1}{5} \times g$$ $$g' = \frac{4}{5} g$$ The period $T$ is given by: $$T = 2\pi \sqrt{\frac{\ell}{g}}$$ The new period $T'$ is: $$\frac{T'}{T} = \sqrt{\frac{g}{g'}} = \sqrt{\frac{g}{\frac{4}{5}g}} = \sqrt{\frac{5}{4}}$$ Therefore: $$T' = 5\sqrt{5}$$

Question 58

Physics · Semiconductor Electronics: Materials, Devices and Simple Circuits · Numerical

A 8 \, $\mathrm{V}$ Zener diode along with a series resistance $R$ is connected across a 20 \, $\mathrm{V}$ supply (as shown in the figure). If the maximum Zener current is 25 \, $\mathrm{mA}$, then the minimum value of $R$ will be _____ \, $\Omega$.

Answer: 480

Solution

Given the equation $\varepsilon - IR - V_z = 0$. Substituting the values, we have: $$20 - IR - 6 = 0$$ Solving for $IR$, we get: $$IR = 12$$ Given $I = 25 \times 10^{-3}$, we substitute to find $R$: $$25 \times 10^{-3} R = 12$$ Solving for $R$, we have: $$R = \frac{12}{25 \times 10^{-3}} = 480 \, \Omega$$

Question 59

Physics · Nuclei · Numerical

Two radioactive materials A and B have decay constants $25\lambda$ and $16\lambda$ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of B to that of A will be "e" after a time $\frac{1}{a\lambda}$. The value of $a$ is________.

Answer: 9

Solution

\[ N=N_0e^{-\lambda t} \] $\frac{N_B}{N_A}$ = $\frac{e^{-\lambda_2 t}}{e^{-\lambda_1 t}}$ = $e^{-\lambda_2 t}e^{\lambda_1 t}$ $e^1$ = $e^{(\lambda_1-\lambda_2)t}$ $(\lambda_1-\lambda_2)$t=1 t = $\frac{1}{\lambda_1-\lambda_2}$ = $\frac{1}{25\lambda-16\lambda}$ = $\frac{1}{9\lambda}$

Question 60

Physics · Alternating Current · Numerical

A capacitor of capacitance $500 \, \mu \mathrm{F}$ is charged completely using a dc supply of $100 \, \mathrm{V}$. It is now connected to an inductor of inductance $50 \, \mathrm{mH}$ to form an LC circuit. The maximum current in LC circuit will be ______ A.

Answer: 10

Solution

Energy stored in capacitor $$= \frac{1}{2} CV^2 = \frac{1}{2} \times 500 \times 10^{-6} \times 10^4$$ $$= \frac{5}{2} \, \mathrm{J}$$ Current will be maximum when whole energy of capacitor becomes energy of inductor. $$\frac{1}{2} LI^2 = \frac{5}{2}$$ $$I = \sqrt{\frac{5}{L}} = \sqrt{\frac{5}{50 \times 10^{-3}}} = 10 \, \mathrm{A}.$$

Chemistry

Question 61

Chemistry · Some Basic Concepts of Chemistry · Single correct

Consider the reaction $4\mathrm{HNO_3}(l)$+$3\mathrm{KCl}(s)$ $\rightarrow$ $\mathrm{Cl_2}(g)$+$\mathrm{NOCl}(g)$+$2\mathrm{H_2O}(g)$+$3\mathrm{KNO_3}(s)$ The amount of $\mathrm{HNO_3}$ required to produce $110.0\ \mathrm{g}$ of $\mathrm{KNO_3}$ is : (Given : Atomic masses of H, O, N and K are $1,\ 16,\ 14$ and $39$, respectively.)

  1. 32.2 g
  2. 69.4 g
  3. 91.5 g
  4. 162.5 g

Answer: (c)

Solution

$4\mathrm{HNO_3}(l)$+$3\mathrm{KCl}(s)$ $\rightarrow$ $\mathrm{Cl_2}(g)$+$\mathrm{NOCl}(g)$+$2\mathrm{H_2O}(g)$+$3\mathrm{KNO_3}(s)$

Question 62

Chemistry · Structure of Atom · Single correct

Given below are the quantum numbers for 4 electrons. A. $n = 3$, $l = 2$, $m_1 = 1$, $m_s = +1/2$ B. $n = 4$, $l = 1$, $m_1 = 0$, $m_s = +1/2$ C. $n = 4$, $l = 2$, $m_1 = -2$, $m_s = -1/2$ D. $n = 3$, $l = 1$, $m_1 = -1$, $m_s = +1/2$ The correct order of increasing energy is :

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

Answer: (b)

Solution

Energy order of subshell decided by $(n+\lambda)$ rule. A $\Rightarrow$ 3d $\Rightarrow n + 1 = 5$ B $\Rightarrow$ 4p $\Rightarrow n + \lambda = 5$ C $\Rightarrow$ 4d $\Rightarrow n + \ell = 6$ D $\Rightarrow$ 3s $\Rightarrow (n+\ell) = 4$ D < A < B < C

Question 63

Chemistry · Some Basic Concepts of Chemistry · Single correct

C(s) + $O_2(g)$ $\rightarrow$ $CO_2(g)$ + 400 $\mathrm{kJ}$ C(s) + $\frac{1}{2}$ $O_2(g)$ $\rightarrow$ CO(g) + 100 $\mathrm{kJ}$ When coal of purity 60$\%$ is allowed to burn in presence of insufficient oxygen, 60$\%$ of carbon is converted into 'CO' and the remaining is converted into '$CO_2$'. The heat generated when 0.6 $\mathrm{kg}$ of coal is burnt is _______.

  1. 1600 $\mathrm{kJ}$
  2. 3200 $\mathrm{kJ}$
  3. 4400 $\mathrm{kJ}$
  4. 6600 $\mathrm{kJ}$

Answer: (d)

Solution

Given the reactions: $$\mathrm{C(S) + O_2(g) \rightarrow CO_2(g) + 400 \, kJ}$$ 1 g mole $$\mathrm{C(s) + \frac{1}{2} O_2 (g) \rightarrow CO(g) + 100 \, kJ} (II)$$ Calculating the mass: $$0.6 \times 1000 = 600 \, \mathrm{gm}$$ $$600 \times \frac{60}{100} (Pure Carbon)$$ $$= 360 \, \mathrm{gm} = \frac{360}{12} = 30 \, mole (Pure Carbon)$$ Carbon converted into $\mathrm{CO_2}$: $$= \left( 30 - 30 \times \frac{60}{100} \right)$$ $$= 12 \, mole$$ And carbon converted into $\mathrm{CO}$: $$= 30 \times \frac{60}{100} = 18 \, mole$$ Energy generated during II equation: $$= 18 \times 100$$ $$= 1800 \, \mathrm{kJ}$$ Energy generated during I reaction: $$= 12 \times 400$$ $$= 4800$$ Total: $$= 1800 + 4800 = 6600 \, \mathrm{kJ}$$

Question 64

Chemistry · Equilibrium · Single correct

200 $\mathrm{mL}$ of 0.01 $\mathrm{M}$ HCl is mixed with 400 $\mathrm{mL}$ of 0.01 $\mathrm{M}$ $H_2\mathrm{SO}_4$. The pH of the mixture is .

  1. 1.14
  2. 1.78
  3. 2.34
  4. 3.02

Answer: (b)

Solution

For the reaction of HCl and $\mathrm{H_2SO_4}$, the concentration of $[\mathrm{H^+}]$ is calculated as follows: $$[\mathrm{H^+}] = \frac{(0.01 \times 200) + (0.01 \times 2 \times 400)}{600}$$ Simplifying the expression: $$= \frac{2 + 8}{600} = \frac{10}{600} = \frac{1}{60}$$ The pH is given by: $$\mathrm{pH} = -\log \left[ \frac{1}{60} \right]$$ Calculating the pH: $$= 1.78$$

Question 65

Chemistry · Surface Chemistry · Single correct

Given below are the critical temperatures of some of the gases: The gas showing least adsorption on a definite amount of charcoal is:

  1. He
  2. CH_4
  3. CO_2
  4. NH_3

Answer: (a)

Solution

More the critical temp. of gas greater is the ease of liquefaction hence greater is the adsorption.

Question 66

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

Liquation process used for tin (Sn), the metal:

  1. is reacted with acid
  2. is dissolved in water
  3. is brought to molten form which is made to flow on a slope
  4. is fused with NaOH.

Answer: (c)

Solution

Liquation process is used for metal having low melting point such as tin in which they are heated and brought to molten state and made to flow down the slope while impurities with higher melting point left on the top.

Question 67

Chemistry · Hydrogen · Single correct

Given below are two statements. Statement I : Stannane is an example of a molecular hydride. Statement II : Stannane is a planar molecule. In the light of the above statement, choose the most appropriate answer from the options given below :

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

Answer: (c)

Solution

SnH$_4$ is non planar molecular hydride. Tetrahedral shape, sp$^3$ hybridisation.

Question 68

Chemistry · The s-Block Elements · Single correct

Portland cement contains 'X' to enhance the setting time. What is 'X'?

  1. $CaSO_4 \cdot \frac{1}{2}H_2O$
  2. $\mathrm{CaSO_4 \cdot 2H_2O}$
  3. $\mathrm{CaSO_4}$
  4. $\mathrm{CaCO_3}$

Answer: (b)

Solution

Gypsum ($\mathrm{CaSO_4.2H_2O}$) is used to enhance setting time in portland cement.

Question 69

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

When borax is heated with CoO on a platinum loop, blue coloured bead formed is largely due to:

  1. B_2O_3
  2. Co(BO_2)_2
  3. CoB_4O_7
  4. Co[B_4O_5(OH)_4]

Answer: (b)

Solution

$Na_2B_4O_7\cdot10H_2O \xrightarrow{\Delta} Na_2B_4O_7+10H_2O$ $Na_2B_4O_7 \xrightarrow{\Delta} 2NaBO_2\ \text{(sodium metaborate)}+B_2O_3$ $B_2O_3+CoO \longrightarrow Co(BO_2)_2\ \text{(cobalt (II) metaborate)}$ Blue Bead

Question 70

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

Which of the following 3d-metal ion will give the lowest enthalpy of hydration ($\Delta_{hyd}H$) when dissolved in water?

  1. $Cr^{2+}$
  2. $Mn^{2+}$
  3. $Fe^{2+}$
  4. $Co^{2+}$

Answer: (b)

Solution

Enthalpy of hydration increases with increase in charge density. $\mathrm{Mn^{+2}}$ has least charge density (as Mn has highest size among the given options) so it will have least enthalpy of hydration.

Question 71

Chemistry · Co-ordination Compounds · Single correct

Octahedral complexes of copper (II) undergo structural distortion (Jahn-Teller). Which one of the given copper (II) complexes will show the maximum structural distortion ? (en=ethylenediamine; $H_2N-CH_2-CH_2-NH_2$)

  1. [$\mathrm{Cu(H_2O)_6}$]$\mathrm{SO_4}$
  2. [$\mathrm{Cu(en)(H_2O)_4}$]$\mathrm{SO_4}$
  3. $\mathrm{cis}$-[$\mathrm{Cu(en)_2Cl_2}$]
  4. $\mathrm{trans}$-[$\mathrm{Cu(en)_2Cl_2}$]

Answer: (a)

Solution

There is unsymmetric filling of $e_g$ subset of $\mathrm{Cu}^{+2}$ ion, while there is symmetrical distribution in $t_{2g}$ set, if the complex has same ligand there will be equal repulsion which leads to symmetrical bond length along $t_{2g}$, but due to uneven filling of electron in $e_g$ subset, either octahedral will be elongated or compressed.

Question 72

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

Dinitrogen is a robust compound, but reacts at high altitude to form oxides. The oxide of nitrogen that can damage plant leaves and retard photosynthesis is :

  1. $NO$
  2. $\mathrm{NO}_3^-$
  3. $\mathrm{NO}_2$
  4. $\mathrm{NO}_2^-$

Answer: (c)

Solution

The reaction is given by: $$\mathrm{N_2(g) + O_2(g) \rightarrow 2NO(g)}$$ Then: $$\mathrm{2NO(g) + O_2(g) \rightarrow 2NO_2(g)}$$ $\mathrm{NO_2}$ damages plant leaves.

Question 73

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

Correct structure of $\gamma$-methylcyclohexane carbaldehyde is :

Answer: (a)

Solution

The compound shown is γ-methyl cyclohexane carbaldehyde.

Question 74

Chemistry · Haloalkanes and Haloarenes · Single correct

Compound $\mathrm{A}$ undergoes the following sequence of reactions to give compound $\mathrm{B}$. The correct structure and chirality of compound $\mathrm{B}$ is: [where $\mathrm{Et}$ is $-\mathrm{C_2H_5}$]

Answer: (c)

Solution

Question 75

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

Given below are two statements. In the light of the above statement, choose the most appropriate answer from the options given below.

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

Answer: (c)

Solution

Having same configuration.

Question 76

Chemistry · Alcohols, Phenols and Ethers · Single correct

When ethanol is heated with conc. $\mathrm{H_2SO_4}$, a gas is produced. The compound formed, when this gas is treated with cold dilute aqueous solution of Baeyer's reagent, is:

  1. Formaldehyde
  2. Formic acid
  3. Glycol
  4. Ethanoic acid

Answer: (c)

Solution

The reaction starts with $\mathrm{CH_3CH_2OH}$ which is treated with concentrated $\mathrm{H_2SO_4}$ and heat $\Delta$ to form $\mathrm{CH_2=CH_2}$. This is then treated with Bayer's Reagent to form glycol, $\mathrm{CH_2(OH)CH_2(OH)}$.

Question 77

Chemistry · Amines · Single correct

The Hinsberg reagent is :

Answer: (a)

Solution

B.S.C (Benzene sulphonyl chloride) is known as Hinsberg Reagent.

Question 78

Chemistry · Polymers · Single correct

Which of the following is NOT a natural polymer?

  1. Protein
  2. Starch
  3. Rubber
  4. Rayon

Answer: (d)

Solution

Rayon is semisynthetic polymer.

Question 79

Chemistry · Biomolecules · Single correct

Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Amylose is insoluble in water. Reason R: Amylose is a long linear molecule with more than 200 glucose units. In the light of the above statements, choose the correct answer from the options given below.

  1. Both A and R are correct and R is the correct explanation of A.
  2. Both A and R are correct and R is NOT the correct explanation of A.
  3. A is correct but R is not correct.
  4. A is not correct but R is correct.

Answer: (d)

Solution

Amylose is water soluble.

Question 80

Chemistry · Redox Reactions · Single correct

A compound 'X' is a weak acid and it exhibits colour change at pH close to the equivalence point during neutralization of NaOH with CH$_3$COOH. Compound 'X' exists in ionized form in basic medium. The compound 'X' is:

  1. methyl orange
  2. methyl red
  3. phenolphthalein
  4. erichrome Black T

Answer: (c)

Solution

Phenolphthalein is a weak acid and gives color in a basic medium.

Question 81

Chemistry · Solutions · Numerical

$x\ \mathrm{g}$ of molecular oxygen $(\mathrm{O_2})$ is mixed with $200\,\mathrm{g}$ of neon $(\mathrm{Ne})$. The total pressure of the non-reactive mixture of $\mathrm{O_2}$ and $\mathrm{Ne}$ in the cylinder is $25\,\mathrm{bar}$. The partial pressure of $\mathrm{Ne}$ is $20\,\mathrm{bar}$ at the same temperature and volume. The value of $x$ is \_\_\_\_. [Given: Molar mass of $\mathrm{O_2} = 32\,\mathrm{g\,mol^{-1}}$. Molar mass of $\mathrm{Ne} = 20\,\mathrm{g\,mol^{-1}}$]

Answer: 80

Solution

Given $\mathrm{O_2 + Ne}$ with $x \, \mathrm{gm}$ and $200 \, \mathrm{gm}$. The total pressure $P_{total} = 25 \, \mathrm{bar}$ and $P_{\mathrm{Ne}} = 20 \, \mathrm{bar}$. The pressure of $\mathrm{O_2}$ is given by: $$P_{\mathrm{O_2}} + P_{\mathrm{Ne}} = 25$$ $$P_{\mathrm{O_2}} = 25 - 20 = 5 \, \mathrm{bar}$$ Using the equation: $$\frac{x}{32} + \frac{200}{20}$$ We have: $$\frac{1}{5} = \frac{\frac{x}{32}}{\frac{x}{32} + 10}$$ Simplifying: $$1 = \frac{x \times 32}{32(x + 320)}$$ Solving for $x$: $$5x = x + 320$$ $$4x = 320$$ $$x = \frac{320}{4} = 80 \, \mathrm{gm}$$

Question 82

Chemistry · Chemical Bonding and Molecular Structure · Numerical

Consider, $PF_5, BrF_5, PCl_3, SF_6, [ICl_4]^-, ClF_3$ and $IF_5$. Amongst the above molecule(s)/ion(s), the number of molecule(s)/ion(s) having $sp^3d^2$ hybridisation is ____.

Answer: 4

Solution

Question 83

Chemistry · Solutions · Numerical

$1.80\,\mathrm{g}$ of solute A was dissolved in $62.5\,\mathrm{cm^3}$ of ethanol and freezing point of the solution was found to be $155.1\,\mathrm{K}$. The molar mass of solute A is \_\_\_\_ $\mathrm{g\,mol^{-1}}$. [Given: Freezing point of ethanol is $156.0\,\mathrm{K}$. Density of ethanol is $0.80\,\mathrm{g\,cm^{-3}}$. Freezing point depression constant of ethanol is $2.00\,\mathrm{K\,kg\,mol^{-1}}$]

Answer: 80

Solution

Mass of $\mathrm{C_2H_5OH} = 62.5 \times 0.8 = 50 \, \mathrm{g}$. $\Delta T_f = K_f \times m$ $$0.9 = 2 \times \frac{1.8 \times 1000}{M_w \times 50}$$ $$M_w = \frac{2 \times 1.8 \times 1000}{0.9 \times 50} = 80$$

Question 84

Chemistry · Electrochemistry · Fill in the blank

For a cell, $\mathrm{Cu(s) | Cu^{2+}(0.001 \, M) | Ag^{+}(0.01 \, M) | Ag(s)}$ the cell potential is found to be $0.43 \, \mathrm{V}$ at $298 \, \mathrm{K}$. The magnitude of standard electrode potential for $\mathrm{Cu^{2+}/Cu}$ is _______ $\times 10^{-2} \, \mathrm{V}$. $\left[ \text{Given: } E^{\Theta}_{\mathrm{Ag^{+}/Ag}} = 0.80 \, \mathrm{V} \text{ and } \frac{2.303RT}{F} = 0.06 \, \mathrm{V} \right]$

Answer: 34

Solution

At anode $$\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+} + 2e^-$$ At cathode $$2\mathrm{Ag}^+ + 2e^- \rightarrow 2\mathrm{Ag}$$ Cell reaction $$\mathrm{Cu} + 2\mathrm{Ag}^+ \rightarrow \mathrm{Cu}^{2+} + 2\mathrm{Ag}$$ $$E_{cell} = E^0_{cell} - \frac{0.06}{2} \log \frac{[\mathrm{Cu}^{2+}]}{[\mathrm{Ag}^+]^2}$$ $$0.43 = E^0_{cell} - \frac{0.06}{2} \log \frac{(0.001)}{(0.01)^2}$$ $$E^0_{cell} = 0.46$$ $$E^0_{cell} = E^0_{\mathrm{Ag}^+/\mathrm{Ag}} - E^0_{\mathrm{Cu}^{2+}/\mathrm{Cu}}$$ $$0.46 = 0.80 - E^0_{\mathrm{Cu}^{2+}/\mathrm{Cu}}$$ $$E^0_{\mathrm{Cu}^{2+}/\mathrm{Cu}} = 0.34 \, volt$$ $$E^0_{\mathrm{Cu}^{2+}/\mathrm{Cu}} = 34 \times 10^{-2}$$

Question 85

Chemistry · Chemical Kinetics and Nuclear Chemistry · Numerical

Assuming 1 $\mu$ g of trace radioactive element X with a half life of 30 years is absorbed by a growing tree. The amount of X remaining in the tree after 100 years is ___ $\times$ 10^{-1} $\mu$ g. [Given : $\ln$ 10 = 2.303; $\log$ 2 = 0.30]

Answer: 1

Solution

Given the equation $$t = \frac{1}{\lambda} \ln \left( \frac{a}{a-x} \right)$$. We have $$100 = \frac{30}{\ln 2} \ln \left( \frac{1}{w} \right)$$. Solving for $$w$$, we get $$\frac{1}{w} = 10$$. Therefore, $$W = 0.1 \times \mu g$$. The answer is $$1 \times 10^{-1} \mu g$$.

Question 86

Chemistry · Co-ordination Compounds · Numerical

Sum of oxidation state (magnitude) and coordination number of cobalt in $Na[Co(bpy)Cl_4]$ is __. (Given bpy = )

Answer: 9

Solution

Coordination no. = 6 Oxidation state = 3 $$6 + 3 = 9$$

Question 87

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

Consider the following sulphure based oxoacids. $\mathrm{H_2SO_3}$, $\mathrm{H_2SO_4}$, $\mathrm{H_2S_2O_8}$ and $\mathrm{H_2S_2O_7}$. Amongst these oxoacids, the number of those with peroxo(O-O) bond is

Answer: 1

Solution

Question 88

Chemistry · Some Basic Concepts of Chemistry · Numerical

A 1.84 $\mathrm{mg}$ sample of polyhydric alcoholic compound 'X' of molar mass 92.0 $\mathrm{g/mol}$ gave 1.344 $\mathrm{mL}$ of $\mathrm{H}_2$ gas at STP. The number of alcoholic hydrogens present in compound 'X' is ____.

Answer: 6

Solution

R(OH)_x $\rightarrow$ $\mathrm{H}$_2 PoAC on H: $$x \left( \frac{1.84 \times 10^{-3}}{92} \right) = \frac{1.344}{22.4} \times 2$$ $$x = \frac{1.344 \times 2 \times 92 \times 1000}{1.84 \times 22400} = 6$$ x = 6

Question 89

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Numerical

The number of stereoisomers formed in a reaction of ($\pm$) Ph(C=O) C(OH)(CN)Ph with HCN is .

Answer: 4

Solution

The reaction of the given compound with HCN results in the formation of a compound with 3 stereoisomers.

Question 90

Chemistry · Chemistry in Everyday Life · Numerical

The number of chlorine atoms in bithionol is ___ .

Answer: 4

Solution

Bithinol contains two benzene rings connected by a sulfur atom. Each benzene ring has two chlorine atoms attached. Therefore, the total number of chlorine atoms is 4.