JEE Main 27 August 2021 Shift 2 question paper with solutions

JEE Main 27 August 2021 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 · Three Dimensional Geometry · Single correct

The angle between the straight lines, whose direction cosines are given by the equations $2l + 2m - n = 0$ and $mn + nl + lm = 0$, is:

  1. $\frac{\pi}{2}$
  2. $\pi - \cos^{-1}\left(\frac{4}{9}\right)$
  3. $\cos^{-1}\left(\frac{8}{9}\right)$
  4. $\frac{\pi}{3}$

Answer: (a)

Solution

Given $n = 2(\ell + m)$. $\ell m + n(\ell + m) = 0$ $\ell m + 2(\ell + m)^2 = 0$ $2\ell^2 + 2m^2 + 5m\ell = 0$ $2\left(\frac{\ell}{m}\right)^2 + 2 + 5\left(\frac{\ell}{m}\right) = 0$ $2t^2 + 5t + 2 = 0$ $(t + 2)(2t + 1) = 0$ $\Rightarrow t = -2; -\frac{1}{2}$ (i) $\frac{\ell}{m} = -2$ $\frac{n}{m} = -2$ $(-2\, m, \, m, \, -2\, m)$ $(-2, \, 1, \, -2)$ (ii) $\frac{\ell}{m} = -\frac{1}{2}$ $n = -2\ell$ $(\ell, \, -2\ell, \, -2\ell)$ $(1, \, -2, \, -2)$ $\cos \theta = \frac{-2 - 2 + 4}{\sqrt{9} \sqrt{9}} = 0 \Rightarrow \theta = \frac{\pi}{2}$

Question 2

Maths · Matrices · Single correct

Let $A = \begin{pmatrix} [x+1] & [x+2] & [x+3] \\ [x] & [x+3] & [x+2] \\ [x] & [x+2] & [x+4] \end{pmatrix}$, where $[t]$ denotes the greatest integer less than or equal to $t$. If $\det(A) = 192$, then the set of values of $x$ is the interval:

  1. [68, 69)
  2. [62, 63)
  3. [65, 66)
  4. [60, 61)

Answer: (b)

Solution

Given the determinant equation: $$\begin{vmatrix} [x+1] & [x+2] & [x+3] \\ [x] & [x+3] & [x+3] \\ [x] & [x+2] & [x+4] \end{vmatrix} = 192$$ Perform the row operations: $$R_1 \rightarrow R_1 - R_3 \& R_2 \rightarrow R_2 - R_3$$ This gives: $$\begin{vmatrix} 1 & 0 & -1 \\ 0 & 1 & -1 \\ [x] & [x] + 2 & [x] + 4 \end{vmatrix} = 192$$ Expanding the determinant, we have: $$2[x] + 6 + [x] = 192 \Rightarrow [x] = 62$$

Question 3

Maths · Inverse Trigonometric Functions · Single correct

Let M and m respectively be the maximum and minimum values of the function $f(x) = \tan^{-1}(\sin x + \cos x)$ in $\left[0, \frac{\pi}{2}\right]$, Then the value of $\tan(M - m)$ is equal to:

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

Answer: (d)

Solution

Let $g(x)=\sin x+\cos x=\sqrt{2}\sin\left(x+\frac{\pi}{4}\right)$ $g(x)\in[1,\sqrt{2}]$ for $x\in\left[0,\frac{\pi}{2}\right]$ $f(x)=\tan^{-1}(\sin x+\cos x)\in\left[\frac{\pi}{4},\tan^{-1}\sqrt{2}\right]$ $\tan\left(\tan^{-1}\sqrt{2}-\frac{\pi}{4}\right) =\frac{\sqrt{2}-1}{1+\sqrt{2}} \times\frac{\sqrt{2}-1}{\sqrt{2}-1} =3-2\sqrt{2}$

Question 4

Maths · Probability · Single correct

Each of the persons A and B independently tosses three fair coins. The probability that both of them get the same number of heads is :

  1. $\frac{1}{8}$
  2. $\frac{5}{8}$
  3. $\frac{5}{16}$
  4. 1

Answer: (c)

Solution

C-I '0' Head TTT $$\left( \frac{1}{2} \right)^3 \left( \frac{1}{2} \right)^3 = \frac{1}{64}$$ C-II '1' head HTT $$\left( \frac{3}{8} \right) \left( \frac{3}{8} \right) = \frac{9}{64}$$ C-III '2' Head HHT $$\left( \frac{3}{8} \right) \left( \frac{3}{8} \right) = \frac{9}{64}$$ C-IV '3' Heads HHH $$\left( \frac{1}{8} \right) \left( \frac{1}{8} \right) = \frac{1}{64}$$ Total probability = $\frac{5}{16}$ .

Question 5

Maths · Differential Equations · Single correct

A differential equation representing the family of parabolas with axis parallel to y-axis and whose length of latus rectum is the distance of the point $(2, -3)$ form the line $3x + 4y = 5$, is given by:

  1. $10 \frac{d^2y}{dx^2} = 11$
  2. $11 \frac{d^2x}{dy^2} = 10$
  3. $10 \frac{d^2x}{dy^2} = 11$
  4. $11 \frac{d^2y}{dx^2} = 10$

Answer: (d)

Solution

Given $\($ $\alpha$ . $\mathrm{R}$ = $\frac{|3(2) + 4(-3) - 5|}{5}$ = $\frac{11}{5}$ $\)$ $\($ (x - h)^2 = $\frac{11}{5}$ (y - k) $\)$ differentiate with respect to $\($ x' $\)$: $\($ 2(x - h) = $\frac{11}{5}$ $\frac{dy}{dx}$ $\)$ again differentiate $\($ 2 = $\frac{11}{5}$ $\frac{d^2y}{dx^2}$ $\)$ $\($ $\frac{11}{dx^2}$ $\frac{d^2y}{dx^2}$ = 10. $\)$

Question 6

Maths · Conic Sections · Single correct

If two tangents drawn from a point $P$ to the parabola $y^2 = 16(x - 3)$ are at right angles, then the locus of point $P$ is :

  1. $x + 3 = 0$
  2. $x + 1 = 0$
  3. $x + 2 = 0$
  4. $x + 4 = 0$

Answer: (b)

Solution

Locus is directrix of parabola $$x - 3 + 4 = 0 \Rightarrow x + 1 = 0$$

Question 7

Maths · Three Dimensional Geometry · Single correct

The equation of the plane passing through the line of intersection of the planes $\vec{r} \cdot (\hat{i} + \hat{j} + \hat{k}) = 1$ and $\vec{r} \cdot (2\hat{i} + 3\hat{j} - \hat{k}) + 4 = 0$ and parallel to the x-axis is:

  1. $\vec{r} \cdot (\hat{j} - 3\hat{k}) + 6 = 0$
  2. $\vec{r} \cdot (\hat{i} + 3\hat{k}) + 6 = 0$
  3. $\vec{r} \cdot (\hat{i} - 3\hat{k}) + 6 = 0$
  4. $\vec{r} \cdot (\hat{j} - 3\hat{k}) - 6 = 0$

Answer: (a)

Solution

Equation of planes are $\vec{r}\cdot(\hat{i}+\hat{j}+\hat{k})-1=0$ $\Rightarrow x+y+z-1=0$ and $\vec{r}\cdot(2\hat{i}+3\hat{j}-\hat{k})+4=0$ $\Rightarrow 2x+3y-z+4=0$ Equation of planes through line of intersection of these planes is $(x+y+z-1)+\lambda(2x+3y-z+4)=0$ $\Rightarrow (1+2\lambda)x+(1+3\lambda)y+(1-\lambda)z-1+4\lambda=0$ But this plane is parallel to $x$-axis whose direction ratios are $(1,0,0)$ $\therefore (1+2\lambda)1+(1+3\lambda)0+(1-\lambda)0=0$ $\lambda=-\dfrac{1}{2}$ $\therefore$ Required plane is $0x+\left(1-\dfrac{3}{2}\right)y+\left(1+\dfrac{1}{2}\right)z-1+4\left(-\dfrac{1}{2}\right)=0$ $\Rightarrow -\dfrac{y}{2}+\dfrac{3}{2}z-3=0$ $\Rightarrow y-3z+6=0$ $\Rightarrow \vec{r}\cdot(\hat{j}-3\hat{k})+6=0$

Question 8

Maths · Differential Equations · Single correct

If the solution curve of the differential equation $(2x - 10y^3) \, dy + y \, dx = 0$, passes through the points $(0, 1)$ and $(2, \beta)$, then $\beta$ is a root of the equation:

  1. $y^5 - 2y - 2 = 0$
  2. $2y^5 - 2y - 1 = 0$
  3. $2y^5 - y^2 - 2 = 0$
  4. $y^5 - y^2 - 1 = 0$

Answer: (d)

Solution

(2x - 10y^3) $\,$ dy + y $\,$ dx = 0 $\Rightarrow$ $\frac{dx}{dy}$ + $\left$( $\frac{2}{y}$ $\right$) x = 10y^2 I. $\ $F. = e^{$\int$ $\frac{2}{y}$ $\,$ dy} = e^{2 $\ln$(y)} = y^2 Solution of D.E. is $\therefore$ $\ $x $\cdot$ y = $\int$ (10y^2) $\,$ y^2 $\cdot$ dy $$xy^2 = \frac{10y^5}{5} + C \Rightarrow xy^2 = 2y^5 + C$$ It passes through (0, 1) $\rightarrow$ 0 = 2 + C $\Rightarrow$ C = -2 $\therefore$ Curve is xy^2 = 2y^5 - 2 Now, it passes through (2, $\beta$) $$2\beta^2 = 2\beta^5 - 2 \Rightarrow \beta^5 - \beta^2 - 1 = 0$$ $\therefore$ $\beta$ is root of an equation y^5 - y^2 - 1 = 0 Ans.

Question 9

Maths · Determinants · Single correct

Let A(a, 0), B(b, 2b + 1) and C(0, b), b $\neq$ 0, bb $\neq$ 1, be points such that the area of triangle ABC is 1 sq. unit, then the sum of all possible values of a is:

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

Answer: (d)

Solution

Given the determinant equation: $$\left| \begin{array}{ccc} \frac{1}{2} & a & 0 \\ b & 2b+1 & 1 \\ 0 & b & 1 \end{array} \right| = 1$$ Expanding the determinant, we have: $$\begin{vmatrix} a & 0 & 1 \\ b & 2b+1 & 1 \\ 0 & b & 1 \end{vmatrix} = \pm 2$$ This simplifies to: $$a(2b + 1 - b) - 0 + 1(b^2 - 0) = \pm 2$$ Thus, $$a = \frac{\pm 2 - b^2}{b+1}$$ Therefore, $$a = \frac{2 - b^2}{b+1} and a = \frac{-2 - b^2}{b+1}$$ The sum of possible values of 'a' is: $$= \frac{-2b^2}{a+1} Ans.$$

Question 10

Maths · Determinants · Single correct

Let [$\lambda$] be the greatest integer less than or equal to $\lambda$. The set of all values of $\lambda$ for which the system of linear equations $x + y + z = 4$, $3x + 2y + 5z = 3$, $9x + 4y + (28 + [\lambda])z = [\lambda]$ has a solution is:

  1. $\mathbb{R}$
  2. (-$\infty$, -9) $\cup$ (-9, $\infty$)
  3. [-9, -8)
  4. (-$\infty$, -9) $\cup$ [-8, $\infty$)

Answer: (a)

Solution

Given the determinant $$D = \begin{vmatrix} 1 & 1 & 1 \\ 3 & 2 & 5 \\ 9 & 4 & 28 + [\lambda] \end{vmatrix}$$ we have: $$= -24 - [\lambda] + 15 = -[\lambda] - 9$$ If $[\lambda] + 9 \neq 0$ then there is a unique solution. If $[\lambda] + 9 = 0$ then $D_1 = D_2 = D_3 = 0$, so there are infinite solutions. Hence $\lambda$ can be any real number.

Question 11

Maths · Complex Numbers and Quadratic Equations · Single correct

The set of all values of $k > -1$, for which the equation $\left(3x^2 + 4x + 3\right)^2 - (k + 1)\left(3x^2 + 4x + 3\right)\left(3x^2 + 4x + 2\right) + k\left(3x^2 + 4x + 2\right)^2 = 0$ has real roots is:

  1. $\left(1,\frac{5}{2}\right]$
  2. $[2,3)$
  3. $\left[-\frac{1}{2},1\right)$
  4. $\left(\frac{1}{2},\frac{3}{2}\right]-\{1\}$

Answer: (a)

Solution

Given equation becomes $$a^2 - (k+1)ab + kb^2 = 0$$ $$a(a-kb) - b(a-kb) = 0$$ $$(a-kb)(a-b) = 0 \Rightarrow a = kb or a = b (reject) $$ Therefore, $a = kb$ Thus, $$3x^2 + 4x + 3 = k \left(3x^2 + 4x + 2\right)$$ $$\Rightarrow 3(k-1)x^2 + 4(k-1)x + (2k-3) = 0$$ For real roots $$D \geq 0$$ $$\Rightarrow 16(k-1)^2 - 4(3(k-1))(2k-3) \geq 0$$ $$\Rightarrow 4(k-1)\{4(k-1) - 3(2k-3)\} \geq 0$$ $$\Rightarrow 4(k-1)\{-2k+5\} \geq 0$$ $$\Rightarrow -4(k-1)\{2k-5\} \geq 0$$ $$\Rightarrow (k-1)(2k-5) \leq 0$$ Therefore, $k \in \left[1, \frac{5}{2}\right]$ Thus, $k \neq 1$ Therefore, $k \in \left(1, \frac{5}{2}\right]$ Ans.

Question 12

Maths · Applications of Derivatives · Single correct

A box open from top is made from a rectangular sheet of dimension $a \times b$ by cutting squares each of side $x$ from each of the four corners and folding up the flaps. If the volume of the box is maximum, then $x$ is equal to:

  1. $\frac{a+b-\sqrt{a^2+b^2-ab}}{12}$
  2. $\frac{a+b-\sqrt{a^2+b^2+ab}}{6}$
  3. $\frac{a+b-\sqrt{a^2+b^2-ab}}{6}$
  4. $\frac{a+b+\sqrt{a^2+b^2-ab}}{6}$

Answer: (c)

Solution

The volume $V$ is given by $V = \ell \cdot b \cdot h = (a - 2x)(b - 2x)x$. Thus, $V(x) = (2x - a)(2x - b)x$. Expanding, $V(x) = 4x^3 - 2(a + b)x^2 + abx$. Differentiating with respect to $x$, we have: $$\frac{d}{dx}V(x) = 12x^2 - 4(a + b)x + ab.$$ Setting the derivative to zero for critical points: $$\frac{d}{dx}(V(x)) = 0 \Rightarrow 12x^2 - 4(a + b)x + ab = 0.$$ This is a quadratic equation in $x$: $$x = \frac{4(a + b) \pm \sqrt{16(a + b)^2 - 48ab}}{2(12)}.$$ Simplifying, we get: $$x = \frac{(a + b) \pm \sqrt{a^2 + b^2 - ab}}{6}.$$ Let $x = \alpha = \frac{6}{(a+b)+\sqrt{a^2+b^2-ab}}$ and $x = \beta = \frac{(a+b)-\sqrt{a^2+b^2-ab}}{6}$. Now, $12(x - \alpha)(x - \beta) = 0$. The sign chart shows that $x = \beta$ is a maximum. Therefore, $x = \beta = \frac{a+b-\sqrt{a^2+b^2-ab}}{b}$.

Question 13

Maths · Mathematical Reasoning · Single correct

The Boolean expression $(p \land q) \Rightarrow ((r \land q) \land p)$ is equivalent to:

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

Answer: (a)

Solution

Given $(p \land q) \Rightarrow ((r \land q) \land p)$ $$\sim (p \land q) \lor ((r \land q) \land p)$$ $$\sim (p \land q) \lor ((r \land q) \land (p \land q))$$ $$\Rightarrow [\sim (p \land q) \lor (p \land q)] \land (\sim (p \land q) \lor (r \land p))$$ $$\Rightarrow t \land [\sim (p \land q) \lor (r \land p)]$$ $$\Rightarrow \sim (p \land q) \lor (r \land p)$$ $$\Rightarrow (p \land q) \Rightarrow (r \land p)$$ Aliter: given statement says "if p and q both happen then p and q and r will happen" it Simply implies "If p and q both happen then 'r' too will happen " i.e. "if p and q both happen then r and p too will happen i.e. $(p \land q) \Rightarrow (r \land p)$

Question 14

Maths · Sets · Single correct

Let $\mathbb{Z}$ be the set of all integers, $A=\left\{(x,y)\in\mathbb{Z}\times\mathbb{Z}:(x-2)^2+y^2\leq4\right\}$ $B=\left\{(x,y)\in\mathbb{Z}\times\mathbb{Z}:x^2+y^2\leq4\right\}$ and $C=\left\{(x,y)\in\mathbb{Z}\times\mathbb{Z}:(x-2)^2+(y-2)^2\leq4\right\}$. If the total number of relations from $A\cap B$ to $A\cap C$ is $2^p$, then the value of $p$ is:

  1. 16
  2. 25
  3. 49
  4. 9

Answer: (b)

Solution

The equations of the circles are given by: $$(x - 2)^2 + y^2 \leq 4$$ $$x^2 + y^2 \leq 4$$ The number of points common in $C_1$ and $C_2$ is 5. The points are $(0, 0)$, $(1, 0)$, $(2, 0)$, $(1, 1)$, $(1, -1)$. Similarly, in $C_2$ and $C_3$ the number of common points is 5. The number of relations is $2^{5 \times 5} = 2^{25}$.

Question 15

Maths · Applications of Integrals · Single correct

The area of the region bounded by the parabola $(y - 2)^2 = (x - 1)$, the tangent to it at the point whose ordinate is 3 and the $x$-axis is:

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

Answer: (a)

Solution

Given $y = 3 \Rightarrow x = 2$. Point is $(2, 3)$. Differentiate with respect to $x$: $$2(y - 2)y' = 1$$ which implies $$y' = \frac{1}{2(y-2)}$$ Therefore, $$y'(2,3) = \frac{1}{2}$$ Thus, $$\frac{y-3}{x-2} = \frac{1}{2} \Rightarrow x - 2y + 4 = 0$$ The area is given by $$\int_{0}^{3} \left( (y-2)^2 + 1 - (2y-4) \right) \, dy$$ which equals $9$ square units.

Question 16

Maths · Inverse Trigonometric Functions · Single correct

If $y(x) = \cot^{-1}\left(\frac{\sqrt{1+\sin x} + \sqrt{1-\sin x}}{\sqrt{1+\sin x} - \sqrt{1-\sin x}}\right), x \in \left(\frac{\pi}{2}, \pi\right),$ then $\frac{dy}{dx}$ at $x = \frac{5\pi}{6}$ is:

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

Answer: (a)

Solution

Given $$y(x) = \cot^{-1} \left[ \frac{\cos \frac{x}{2} + \sin \frac{x}{2} - \sin \frac{x}{2} - \cos \frac{x}{2}}{\cos \frac{x}{2} + \sin \frac{x}{2} - \sin \frac{x}{2} + \cos \frac{x}{2}} \right]$$ Simplifying, $$y(x) = \cot^{-1} \left( \tan \frac{x}{2} \right) = \frac{\pi}{2} - \frac{x}{2}$$ Differentiating, $$y'(x) = -\frac{1}{2}$$

Question 17

Maths · Heights and Distances · Single correct

Two poles, AB of length $a$ metres and CD of length $a + b$ $(b \neq a)$ metres are erected at the same horizontal level with bases at $B$ and $D$. If $BD = x$ and $\tan \angle ACB = \frac{1}{2}$, then:

  1. $x^2 + 2(a + 2b)x - b(a + b) = 0$
  2. $x^2 + 2(a + 2b)x + a(a + b) = 0$
  3. $x^2 - 2ax + b(a + b) = 0$
  4. $x^2 - 2ax + a(a + b) = 0$

Answer: (c)

Solution

Given $\tan \theta = \frac{1}{2}$. $\tan(\theta + \alpha) = \frac{x}{b}$, $\tan \alpha = \frac{x}{a+b}$. Therefore, $$\frac{1}{2} + \frac{x}{a+b}$$ implies $$\frac{\frac{1}{2} + \frac{x}{a+b}}{1 - \frac{1}{2} \cdot \frac{x}{a+b}} = \frac{x}{b}.$$ This leads to $$x^2 - 2ax + ab + b^2 = 0.$$

Question 18

Maths · Sequences and Series · Single correct

If $0 < x < 1$ and $y = \frac{1}{2}x^2 + \frac{2}{3}x^3 + \frac{3}{4}x^4 + \ldots$, then the value of $e^{1+y}$ at $x = \frac{1}{2}$ is:

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

Answer: (a)

Solution

Given $$y = \left(1 - \frac{1}{2}\right)x^2 + \left(1 - \frac{1}{3}\right)x^3 + \ldots$$ This can be rewritten as $$= \left(x^2 + x^3 + x^4 + \ldots\right) - \left(\frac{x^2}{2} + \frac{x^3}{3} + \frac{x^4}{4} + \ldots\right)$$ Simplifying further, we have $$= \frac{x^2}{1-x} + x - \left(x + \frac{x^2}{2} + \frac{x^2}{3} + \ldots\right)$$ This simplifies to $$= \frac{x}{1-x} + \ln(1-x)$$ Substituting $x = \frac{1}{2}$, we get $$y = 1 - \ln 2$$ Thus, $$e^{1+y} = e^{1+1-\ln 2}$$ This equals $$= e^{2-(\ln 2)} = \frac{e^2}{2}$$

Question 19

Maths · Integrals · Single correct

The value of the integral $\int_0^1 \frac{\sqrt{x} \, dx}{(1+x)(1+3x)(3+x)}$ is:

  1. $\\frac{\\pi}{8} \\left( 1 - \\frac{\\sqrt{3}}{2} \\right)$
  2. $\\frac{\\pi}{4} \\left( 1 - \\frac{\\sqrt{3}}{6} \\right)$
  3. $\\frac{\\pi}{8} \\left( 1 - \\frac{\\sqrt{3}}{6} \\right)$
  4. $\\frac{\\pi}{4} \\left( 1 - \\frac{\\sqrt{3}}{2} \\right)$

Answer: (a)

Solution

Given $$I = \int_0^1 \frac{\sqrt{x}}{(1+x)(1+3x)(3+x)} \, dx$$ Let $x = t^2 \Rightarrow dx = 2t \cdot dt$ $$I = \int_0^1 \frac{t(2t)}{(t^2+1)(1+3t^2)(3+t^2)} \, dt$$ $$I = \int_0^1 \frac{(3t^2+1) - (t^2+1)}{(3t^2+1)(t^2+1)(3+t^2)} \, dt$$ $$I = \int_0^1 \frac{dt}{(t^2+1)(3+t^2)} - \int_0^1 \frac{dt}{(1+3t^2)(3+t^2)}$$ $$= \frac{1}{2} \int_0^1 \frac{dt}{t^2+1} - \frac{1}{2} \int_0^1 \frac{dt}{t^2+3} + \frac{1}{8} \int_0^1 \frac{dt}{t^2+3} - \frac{3}{8} \int_0^1 \frac{dt}{1+3t^2}$$ $$= \frac{1}{2} \int_0^1 \frac{dt}{t^2+1} - \frac{3}{8} \int_0^1 \frac{dt}{t^2+3} - \frac{3}{8} \int_0^1 \frac{dt}{1+3t^2}$$ $$= \frac{1}{2} \left( \tan^{-1}(t) \right)_0^1 - \frac{3}{8\sqrt{3}} \left( \tan^{-1} \left( \frac{t}{\sqrt{3}} \right) \right)_0^1$$ $$- \frac{3}{8\sqrt{3}} \left( \tan^{-1}(\sqrt{3}t) \right)_0^1$$ $$= \frac{1}{2} \left( \frac{\pi}{4} \right) - \frac{\sqrt{3}}{8} \left( \frac{\pi}{6} \right) - \frac{\sqrt{3}}{8} \left( \frac{\pi}{3} \right)$$ $$= \frac{\pi}{8} - \frac{\sqrt{3}}{16} \pi$$ $$= \frac{\pi}{8} \left( 1 - \frac{\sqrt{3}}{2} \right)$$

Question 20

Maths · Limits and Derivatives · Single correct

If $\lim_{x \to \infty} \left( \sqrt{x^2 - x + 1 - ax} \right) = b$, then the ordered pair $(a, b)$ is:

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

Answer: (b)

Solution

Given $\($ $\lim$_{x $\to$ $\infty$} $\left$( $\sqrt{x^2 - x + 1}$ - ax $\right$) = b $\)$ ($\($ $\infty$ - $\infty$ $\)$). This implies $\($ a > 0 $\)$. Now, $\($ $\lim$_{x $\to$ $\infty$} $\frac{x^2 - x + 1 - a^2 x^2}{\sqrt{x^2 - x + 1} + ax}$ = b $\)$. $\($ $\Rightarrow$ $\lim$_{x $\to$ $\infty$} $\frac{(1-a^2)x^2 - x + 1}{\sqrt{x^2 - x + 1} + ax}$ = b $\)$. $\($ $\Rightarrow$ $\lim$_{x $\to$ $\infty$} $\frac{(1-a^2)x^2 - x + 1}{x \left( \sqrt{1 - \frac{1}{x} + \frac{1}{x^2}} + a \right)}$ = b $\)$. $\($ $\Rightarrow$ 1 - a^2 = 0 $\Rightarrow$ a = 1 $\)$. Now, $\($ $\lim$_{x $\to$ $\infty$} $\frac{-x + 1}{x \left( \sqrt{1 - \frac{1}{x} + \frac{1}{x^2}} + a \right)}$ = b $\)$. $\($ $\Rightarrow$ $\frac{-1}{1 + a}$ = b $\Rightarrow$ b = -$\frac{1}{2}$ $\)$. Thus, $\($(a, b) = $\left$(1, -$\frac{1}{2}$$\right$)$\)$.

Question 21

Maths · Trigonometric Functions · Numerical

Let S be the sum of all solutions (in radians) of the equation $\sin^4 \theta + \cos^4 \theta - \sin \theta \cos \theta = 0$ in $[0, 4\pi]$. Then $\frac{8S}{\pi}$ is equal to .

Answer: 56

Solution

Given equation $$\sin^4 \theta + \cos^4 \theta - \sin \theta \cos \theta = 0$$ This implies $$1 - \sin^2 \theta \cos^2 \theta - \sin \theta \cos \theta = 0$$ which simplifies to $$2 - (\sin 2\theta)^2 - \sin 2\theta = 0$$ Rearranging gives $$(\sin 2\theta)^2 + (\sin 2\theta) - 2 = 0$$ Factoring, we have $$(\sin 2\theta + 2)(\sin 2\theta - 1) = 0$$ Thus, $$\sin 2\theta = 1 or \sin 2\theta = -2 (not possible)$$ Therefore, $$2\theta = \frac{\pi}{2}, \frac{5\pi}{2}, \frac{9\pi}{2}, \frac{13\pi}{2}$$ This gives $$\theta = \frac{\pi}{4}, \frac{5\pi}{4}, \frac{9\pi}{4}, \frac{13\pi}{4}$$ Summing these, we find $$S = \frac{\pi}{4} + \frac{5\pi}{4} + \frac{9\pi}{4} + \frac{13\pi}{4} = 7\pi$$ Finally, $$\frac{8S}{\pi} = \frac{8 \times 7\pi}{\pi} = 56.00$$

Question 22

Maths · Three Dimensional Geometry · Numerical

Let $S$ be the mirror image of the point $Q(1, 3, 4)$ with respect to the plane $2x - y + z + 3 = 0$ and let $R(3, 5, \gamma)$ be a point of this plane. Then the square of the length of the line segment $SR$ is .

Answer: 72

Solution

Since $R(3, 5, \gamma)$ lies on the plane $2x - y + z + 3 = 0$. Therefore, $6 - 5 + \gamma + 3 = 0$ implies $\gamma = -4$. Now, direction ratios of line $QS$ are $2, -1, 1$. The equation of line $QS$ is $$\frac{x-1}{2} = \frac{y-3}{-1} = \frac{z-4}{1} = \lambda (say)$$ implies $F(2\lambda + 1, -\lambda + 3, \lambda + 4)$. F lies in the plane $$2(2\lambda + 1) - (-\lambda + 3) + (\lambda + 4) + 3 = 0$$ $$\Rightarrow 4\lambda + 2 + \lambda - 3 + \lambda + 7 = 0$$ $$\Rightarrow 6\lambda + 6 = 0 \Rightarrow \lambda = -1$$ implies $F(-1, 4, 3)$. Since, $F$ is the midpoint of $QS$. Therefore, coordinates of $S$ are $(-3, 5, 2)$. So, $SR = \sqrt{36 + 0 + 36} = \sqrt{72}$. $SR^2 = 72$.

Question 23

Maths · Probability · Numerical

The probability distribution of random variable X is given by: \begin{tabular}{|c|c|c|c|c|c|} \hline X & 1 & 2 & 3 & 4 & 5 \\ \hline P(X) & K & 2K & 2K & 3K & K \\ \hline \end{tabular} Let p = P(1 < X < 4 $\mid$ X < 3). If 5p = $\lambda$ K, then $\lambda$ equal to .

Answer: 30

Solution

Given $\sum \mathrm{P}(X) = 1 \Rightarrow k + 2k + 2k + 3k + k = 1$. Therefore, $k = \frac{1}{9}$. Now, $p = \mathrm{P}\left(\frac{kX<4}{X<3}\right) = \frac{\mathrm{P}(X=2)}{\mathrm{P}(X<3)} = \frac{2k}{k + 9k} = \frac{2k}{9k} = \frac{2}{3}$. Thus, $p = \frac{2}{3}$. Now, $5p = \lambda k$. Therefore, $(5)\left(\frac{2}{3}\right) = \lambda (1/9)$. Thus, $\lambda = 30$.

Question 24

Maths · Complex Numbers and Quadratic Equations · Numerical

Let $z_1$ and $z_2$ be two complex numbers such that $\arg(z_1 - z_2) = \frac{\pi}{4}$ and $z_1, z_2$ satisfy the equation $$|z - 3| = \Re(z).$$ Then the imaginary part of $z_1 + z_2$ is equal to .

Answer: 6

Solution

Given $|z - 3| = \mathrm{Re}(z)$. Let $Z = x = iy$. $$\Rightarrow (x - 3)^2 + y^2 = x^2$$ $$\Rightarrow x^2 + 9 - 6x + y^2 = x^2$$ $$\Rightarrow y^2 = 6x - 9$$ $$\Rightarrow y^2 = 6 \left( x - \frac{3}{2} \right)$$ $z_1$ and $z_2$ lie on the parabola mentioned in eq.(1). $$\arg(z_1 - z_2) = \frac{\pi}{4}$$ $$\Rightarrow Slope of PQ = 1.$$ Let $P \left( \frac{3}{2} + \frac{3}{2} t_1^2, 3t_1 \right)$ and $Q \left( \frac{3}{2} + \frac{3}{2} t_2^2, 3t_2 \right)$. Slope of $PQ = \frac{3(t_2 - t_1)}{\frac{3}{2} (t_2^2 - t_1^2)} = 1$ $$\Rightarrow \frac{2}{t_2 + t_1} = 1$$ $$\Rightarrow t_2 + t_1 = 2$$ $$\mathrm{Im}(z_1 + z_2) = 3t_1 + 3t_2 = 3(t_1 + t_2) = 3(2)$$ Ans. 6.00 Aliter: Let $z_1 = x_1 + iy_1; z_2 = x_2 + iy_2$. $z_1 - z_2 = (x_1 - x_2) + i (y_1 - y_2)$ $$\therefore \arg(z_1 - z_2) = \frac{\pi}{4} \Rightarrow \tan^{-1} \left( \frac{y_1 - y_2}{x_1 - x_2} \right) = \frac{\pi}{4}$$ $$y_1 - y_2 = x_1 - x_2 (1)$$ $$|z_1 - 3| = \mathrm{Re}(z_1) \Rightarrow (x_1 - 3)^2 + y_1^2 = x_1^2 (2)$$ $$|z_2 - 3| = \mathrm{Re}(z_2) \Rightarrow (x_2 - 3)^2 + y_2^2 = x_2^2 (3)$$ Sub (2) & (3) $$(x_1 - 3)^2 - (x_2 - 3)^2 + y_1^2 - y_2^2 = x_1^2 - x_2^2$$ $$(x_1 - x_2)(x_1 + x_2 - 6) + (y_1 - y_2)(y_1 + y_2) = (x_1 - x_2)(x_1 + x_2)$$ $$x_1 + x_2 - 6 + y_1 + y_2 = x_1 + x_2 \Rightarrow y_1 + y_2 = 6.$$

Question 25

Maths · Sets · Numerical

Let S = $\{1, 2, 3, 4, 5, 6, 9\}$. Then the number of elements in the set T = $\{$A $\subseteq$ S : A $\neq$ $\phi$ and the sum of all the elements of A is not a multiple of 3$\}$ is .

Answer: 80

Solution

3n type $\rightarrow 3, 6, 9 = P$ 3n - 1 type $\rightarrow 2, 5 = Q$ 3n - 2 type $\rightarrow 1, 4 = R$ Number of subset of $S$ containing one element which are not divisible by 3 $= \binom{2}{1} + \binom{2}{1} = 4$ Number of subset of $S$ containing two numbers whose sum is not divisible by 3 $$= \binom{3}{1} \times \binom{2}{1} + \binom{3}{1} \times \binom{2}{1} + \binom{2}{2} + \binom{2}{2} = 14$$ Number of subsets containing 3 elements whose sum is not divisible by 3 $$= \binom{3}{2} \times \binom{4}{1} + \left( \binom{2}{2} \times \binom{2}{1} \right) 2 + \binom{3}{1} \left( \binom{2}{2} + \binom{2}{2} \right) = 22$$ Number of subsets containing 4 elements whose sum is not divisible by 3 $$= \binom{3}{3} \times \binom{4}{1} + \binom{3}{2} \left( \binom{2}{2} + \binom{2}{2} \right) + \left( \binom{3}{1} \binom{2}{1} \times \binom{2}{1} \right) 2$$ $$= 4 + 6 + 12 = 22.$$ Number of subsets of $S$ containing 5 elements whose sum is not divisible by 3. $$= \binom{3}{3} \left( \binom{2}{2} + \binom{2}{2} \right) + \left( \binom{3}{2} \binom{2}{1} \times \binom{2}{2} \right) \times 2 = 2 + 12 = 14$$ Number of subsets of $S$ containing 6 elements whose sum is not divisible by 3 $= 4$ $\Rightarrow$ Total subsets of Set $A$ whose sum of digits is not divisible by 3 $= 4 + 14 + 22 + 22 + 14 + 4 = 80.$

Question 26

Maths · Conic Sections · Numerical

Let A($\sec \theta$, $2 \tan \theta$) and B($\sec \phi$, $2 \tan \phi$), where $\theta + \phi = \pi/2$, be two points on the hyperbola $2x^2 - y^2 = 2$. If $(\alpha, \beta)$ is the point of the intersection of the normals to the hyperbola at A and B, then $(2\beta)^2$ is equal to .

Answer: 36

Solution

Since, point $A(\sec \theta, 2 \tan \theta)$ lies on the hyperbola $$2x^2 - y^2 = 2$$ Therefore, $2 \sec^2 \theta - 4 \tan^2 \theta = 2$ $$\Rightarrow 2 + 2 \tan^2 \theta - 4 \tan^2 \theta = 2$$ $$\Rightarrow \tan \theta = 0 \Rightarrow \theta = 0$$ Similarly, for point $B$, we will get $\phi = 0$. But according to question $\theta + \phi = \frac{\pi}{2}$ which is not possible. Hence it must be a 'BONUS'.

Question 27

Maths · Conic Sections · Numerical

Two circles each of radius 5 units touch each other at the point (1, 2). If the equation of their common tangent is $4x + 3y = 10$, and $C_1(\alpha, \beta)$ and $C_2(\gamma, \delta)$, $C_1 \neq C_2$ are their centres, then $| (\alpha + \beta)(\gamma + \delta) |$ is equal to .

Answer: 40

Solution

Slope of line joining centres of circles $= \frac{4}{3} = \tan \theta$. $$\Rightarrow \cos \theta = \frac{3}{5}, \sin \theta = \frac{4}{5}$$ Now using parametric form $$\frac{x-1}{\cos \theta} = \frac{y-2}{\sin \theta} = \pm 5$$ $\oplus$ $(x, y) = (1 + 5 \cos \theta, 2 + 5 \sin \theta)$ $(\alpha, \beta) = (4, 6)$ $\Theta(x, y) = (\gamma, \delta) = (1 - 5 \cos \theta, 2 - 5 \sin \theta)$ $(\gamma, s) = (-2, -2)$ $$\Rightarrow |(\alpha + \beta)(\gamma + \delta)| = |10x - 4| = 40$$

Question 28

Maths · Basics Of Mathematics · Numerical

3 $\times$ 7^{22} + 2 $\times$ 10^{22} - 44 when divided by 18 leaves the remainder.

Answer: 15

Solution

Given $$3(1+6)^{22} + 2 \cdot (1+9)^{22} - 44 = (3+2-44) = 18 \cdot I$$ $$= -39 + 18 \cdot I$$ $$= (54 - 39) + 18(I - 3)$$ $$= 15 + 18I_1$$ Therefore, the remainder is 15.

Question 29

Maths · Statistics · Numerical

An online exam is attempted by 50 candidates out of which 20 are boys. The average marks obtained by boys is 12 with a variance 2. The variance of marks obtained by 30 girls is also 2. The average marks of all 50 candidates is 15. If $\mu$ is the average marks of girls and $\sigma^2$ is the variance of marks of 50 candidates, then $\mu + \sigma^2$ is equal to .

Answer: 25

Solution

Given $\sigma_b^2 = 2$ (variance of boys) $n_1 = no. of boys$. $\bar{x}_b = 12$ and $n_2 = no. of girls$. $\sigma_g^2 = 2$. $\bar{x}_g = \frac{50 \times 15 - 12 \times \sigma_b}{30} = \frac{750 - 12 \times 20}{30} = 17 = \mu$. Variance of combined series: $$\sigma^2 = \frac{n_1 \sigma_b^2 + n_2 \sigma_g^2}{n_1 + n_2} + \frac{n_1 n_2}{(n_1 + n_2)^2} \left( \bar{x}_b - \bar{x}_g \right)^2$$ $$\sigma^2 = \frac{20 \times 2 + 30 \times 2}{20 + 30} + \frac{20 \times 30}{(20 + 30)^2} (12 - 17)^2$$ $$\sigma^2 = 8.$$ Therefore, $\mu + \sigma^2 = 17 + 8 = 25$.

Question 30

Maths · Integrals · Numerical

If $$\int \frac{2e^x + 3e^{-x}}{4e^x + 7e^{-x}} \, dx = \frac{1}{14} \left( ux + v \log_e (4e^x + 7e^{-x}) \right) + C,$$ where C is a constant of integration, then $u + v$ is equal to .

Answer: 7

Solution

Given $$\int \frac{2e^x}{4e^x + 7e^{-x}} \, dx + 3 \int \frac{e^{-x}}{4e^x + 7e^{-x}} \, dx$$ Let $4e^x + 7 = T$ $$8e^x \, dx = dT$$ $$2e^x \, dx = \frac{dT}{4}$$ Let $4 + 7e^{-2x} = t$ $$-14e^{-2x} \, dx = dt$$ $$e^{-2x} \, dx = -\frac{dt}{14}$$ $$\int \frac{dT}{4T} - \frac{3}{14} \int \frac{dt}{t}$$ $$= \frac{1}{4} \log T - \frac{3}{14} \log t + C$$ $$= \frac{1}{4} \log (4e^x + 7) - \frac{3}{14} \log (4 + 7e^{-2x}) + C$$ $$= \frac{1}{14} \left[ \frac{1}{2} \log (4e^x + 7e^{-x}) + \frac{13}{2} x \right] + C$$ $$u = \frac{13}{2}, \; v = \frac{1}{2} \Rightarrow u + v = 7$$ Aliter: $$2e^x + 3e^{-x} = A (4e^x + 7e^{-x}) + B (4e^x - 7e^{-x}) + \lambda$$ $$2 = 4A + 4B; 3 = 7A - 7B; \; \lambda = 0$$ $$A + B = \frac{1}{2}$$ $$A - B = \frac{3}{7}$$ $$A = \frac{1}{2} \left( \frac{1}{2} + \frac{3}{7} \right) = \frac{7 + 6}{28} = \frac{13}{28}$$ $$B = A - \frac{3}{7} = \frac{13}{28} - \frac{3}{7} = \frac{13 - 12}{28} = \frac{1}{28}$$ $$\int \frac{5}{28} \, dx + \frac{1}{28} \int \frac{4e^x - 7e^{-x}}{4e^x + 7e^{-x}} \, dx$$ $$\frac{13}{28} x + \frac{1}{28} \ln |4e^x + 7e^{-x}| + C$$ $$u = \frac{13}{2}, \; v = \frac{1}{2}$$ $$\Rightarrow u + v = 7$$

Physics

Question 31

Physics · Ray Optics and Optical Instruments · Single correct

Curved surfaces of a plano-convex lens of refractive index $\mu_1$ and a plano-concave lens of refractive index $\mu_2$ have equal radius of curvature as shown in figure. Find the ratio of radius of curvature to the focal length of the combined lenses.

  1. $\frac{1}{\mu_2 - \mu_1}$
  2. $\mu_1 - \mu_2$
  3. $\frac{1}{\mu_1 - \mu_2}$
  4. $\mu_2 - \mu_1$

Answer: (b)

Solution

The equations for the focal lengths are given by: $$\frac{1}{f_1} = (\mu_1 - 1) \left(\frac{1}{R}\right)$$ $$\frac{1}{f_2} = (\mu_2 - 1) \left(-\frac{1}{R}\right)$$ Adding these equations, we have: $$\frac{1}{f_1} + \frac{1}{f_2} = \frac{1}{f_{eq}} = \frac{(\mu_1 - 1) - (\mu_2 - 1)}{R}$$ Simplifying, we get: $$\frac{1}{f_{eq}} = \frac{(\mu_1 - \mu_2)}{R}$$ Therefore, the equivalent focal length is: $$\frac{R}{f_{eq}} = (\mu_1 - \mu_2)$$

Question 32

Physics · Laws of Motion · Single correct

The boxes of masses 2 kg and 8 kg are connected by a massless string passing over smooth pulleys. Calculate the time taken by box of mass 8 kg to strike the ground starting from rest. (use $g = 10 \, \mathrm{m/s^2}$)

  1. 0.34 s
  2. 0.2 s
  3. 0.25 s
  4. 0.4 s

Answer: (d)

Solution

$(m_{1}g-2T)=m_{1}a \qquad (1)$ $T-m_{2}g=m_{2}(2a)$ $2T-2m_{2}g=4m_{2}a \qquad (2)$ From (1) and (2), $m_{1}g-2m_{2}g=(m_{1}+4m_{2})a$ $a=\frac{(8-4)g}{(8+8)}$ $=\frac{4}{16}g$ $=\frac{g}{4}$ $a=\frac{10}{4}\ \mathrm{m/s^{2}}$ $S=\frac{1}{2}at^{2}$ $0.2=\frac{1}{2}\times\frac{10}{4}\times t^{2}$ $\frac{0.2\times2\times4}{10}=t^{2}$ $t=0.4\ \mathrm{s}$

Question 33

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

For a transistor $\alpha$ and $\beta$ are given as $\alpha = \frac{I_C}{I_E}$ and $\beta = \frac{I_C}{I_B}$. Then the correct relation between $\alpha$ and $\beta$ will be:

  1. $\alpha = \frac{1-\beta}{\beta}$
  2. $\beta = \frac{\alpha}{1-\alpha}$
  3. $\alpha \beta = 1$
  4. $\alpha = \frac{\beta}{1-\beta}$

Answer: (b)

Solution

Given $\alpha = \frac{I_C}{I_E}$, $\beta = \frac{I_C}{I_B}$; $I_E = I_C + I_B$. $$\alpha = \frac{I_C}{I_C + I_B} = \frac{I_C / I_B}{I_C / I_B + 1} = \frac{\beta}{\beta + 1}$$ $$1 + \frac{1}{\beta} = \frac{1}{\alpha}$$ $$\frac{1}{\beta} = \frac{1 - \alpha}{\alpha}$$ $$\beta = \frac{\alpha}{1 - \alpha}$$

Question 34

Physics · Motion in a Straight Line · Single correct

Water drops are falling from a nozzle of a shower onto the floor, from a height of 9.8 m. The drops fall at a regular interval of time. When the first drop strikes the floor, at that instant, the third drop begins to fall. Locate the position of second drop from the floor when the first drop strikes the floor.

  1. 4.18 m
  2. 2.94 m
  3. 2.45 m
  4. 7.35 m

Answer: (d)

Solution

Given $H = \frac{1}{2} g t^2$. $$\frac{9.8 \times 2}{9.8} = t^2$$ $t = \sqrt{2} sec$ $\Delta t$: time interval between drops $h = \frac{1}{2} g (\sqrt{2} - \Delta t)^2$ $0 = \frac{1}{2} g (\sqrt{2} - 2 \Delta t)^2$ $\Delta t = \frac{1}{\sqrt{2}}$ $h = \frac{1}{2} g \left( \sqrt{2} - \frac{1}{\sqrt{2}} \right)^2 = \frac{1}{2} \times 9.8 \times \frac{1}{2} = \frac{9.8}{4} = 2.45 \, m$ $H - h = 9.8 - 2.45 = 7.35 \, m$

Question 35

Physics · System of Particles and Rotational Motion · Single correct

Two discs have moments of inertia $I_1$ and $I_2$ about their respective axes perpendicular to the plane and passing through the centre. They are rotating with angular speeds, $\omega_1$ and $\omega_2$ respectively and are brought into contact face to face with their axes of rotation coaxial. The loss in kinetic energy of the system in the process is given by:

  1. $\frac{I_1 I_2}{(I_1 + I_2)} (\omega_1 - \omega_2)^2$
  2. $\frac{(I_1 - I_2)^2 \omega_1 \omega_2}{2(I_1 + I_2)}$
  3. $\frac{I_1 I_2}{2(I_1 + I_2)} (\omega_1 - \omega_2)^2$
  4. $\frac{(\omega_1 - \omega_2)^2}{2(I_1 + I_2)}$

Answer: (c)

Solution

From conservation of angular momentum we get $$I_1 \omega_1 + I_2 \omega_2 = (I_1 + I_2) \omega$$ $$\omega = \frac{I_1 \omega_1 + I_2 \omega_2}{I_1 + I_2}$$ $$k_i = \frac{1}{2} I_1 \omega_1^2 + \frac{1}{2} I_2 \omega_2^2$$ $$k_f = \frac{1}{2} (I_1 + I_2) \omega^2$$ $$k_i - k_f = \frac{1}{2} \left[ I_1 \omega_1^2 + I_2 \omega_2^2 - \frac{(I_1 \omega_1 + I_2 \omega_2)^2}{I_1 + I_2} \right]$$ Solving above we get $$k_i - k_f = \frac{1}{2} \left( \frac{I_1 I_2}{I_1 + I_2} \right) (\omega_1 - \omega_2)^2$$

Question 36

Physics · Electrostatic Potential and Capacitance · Single correct

Three capacitors $C_1 = 2\mu F$, $C_2 = 6\mu F$ and $C_3 = 12\mu F$ are connected as shown in figure. Find the ratio of the charges on capacitors $C_1$, $C_2$ and $C_3$ respectively: A

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

Answer: (c)

Solution

$(V_D - V) C_2 + (V_D - 0) C_3 = 0$ $(V_D - V) 6 + (V_D - 0) 12 = 0$ $V_D - V + 2V_D = 0$ $$V_D = \frac{V}{3}$$ $q_2 = (V - V_D) C_2$ $$= \left( V - \frac{V}{3} \right) (6 \,\mu F)$$ $$q_2 = (4V)\,\mu F$$ $q_3 = (V_D - 0) C_3$ $$= \frac{V}{3} \times 12\,\mu F$$ $$= 4V\,\mu F$$ $q_1 = (V - 0) C_1$ $$= V (2\,\mu F)$$ $$q_1 : q_2 : q_3 = 2 : 4 : 4$$ $$q_1 : q_2 : q_3 = 1 : 2 : 2$$

Question 37

Physics · Current Electricity · Single correct

The colour coding on a carbon resistor is shown in the given figure. The resistance value of the given resistor is :

  1. $(5700 \pm 285)\,\Omega$
  2. $(7500 \pm 750)\,\Omega$
  3. $(5700 \pm 375)\,\Omega$
  4. $(7500 \pm 375)\,\Omega$

Answer: (d)

Solution

Given $R = 75 \times 10^2 \pm 5\%$ of $7500$. Calculating, $R = (7500 \pm 375) \, \Omega$.

Question 38

Physics · Communication Systems · Single correct

An antenna is mounted on a 400 m tall building. What will be the wavelength of signal of signal that can be radiated effectively by the transmission tower upto a range of 44 km ?

  1. 37.8 m
  2. 605 m
  3. 75.6 m
  4. 302 m

Answer: (b)

Solution

Given $h$: height of antenna and $\lambda$: wavelength of signal. $h h$ $\lambda > 400 \, \mathrm{m}$

Question 39

Physics · Kinetic Theory · Single correct

If the rms speed of oxygen molecules at $0^\circ \mathrm{C}$ is $160 \, \mathrm{m/s}$, find the rms speed of hydrogen molecules at $0^\circ \mathrm{C}$.

  1. 640 $\,$ $\mathrm{m/s}$
  2. 40 $\,$ $\mathrm{m/s}$
  3. 80 $\,$ $\mathrm{m/s}$
  4. 332 $\,$ $\mathrm{m/s}$

Answer: (a)

Solution

The root mean square velocity $V_{rms}$ is given by $$V_{rms} = \sqrt{\frac{3kT}{M}}$$ The ratio of $V_{rms}$ for $\mathrm{O_2}$ and $\mathrm{H_2}$ is $$\left( V_{rms} \right)_{\mathrm{O_2}} / \left( V_{rms} \right)_{\mathrm{H_2}} = \sqrt{\frac{M_{\mathrm{H_2}}}{M_{\mathrm{O_2}}}} = \sqrt{\frac{2}{32}}$$ The velocity of $\mathrm{H_2}$ is $$\left( V_{mm} \right)_{\mathrm{H_2}} = 4 \times \left( V_{mms} \right)_{\mathrm{O_2}}$$ Calculating gives $$= 4 \times 160$$ $$= 640 \, \mathrm{m/s}$$

Question 40

Physics · Electromagnetic Induction · Single correct

A constant magnetic field of 1 T is applied in the $x > 0$ region. A metallic circular ring of radius 1 m is moving with a constant velocity of 1 m/s along the $x$-axis. At $t = 0$ s, the centre of $O$ of the ring is at $x = -1$ m. What will be the value of the induced emf in the ring at $t = 1$ s? (Assume the velocity of the ring does not change.)

  1. 1 V
  2. $2\pi V$
  3. 2 V
  4. 0 V

Answer: (c)

Solution

Given the formula for emf as $emf = BLV$. Substituting the values, we have: $$emf = 1 \cdot (2R) \cdot 1$$ $$= 2 \, \mathrm{V}$$

Question 41

Physics · Gravitation · Single correct

A mass of 50 kg is placed at the centre of a uniform spherical shell of mass 100 kg and radius 50 m. If the gravitational potential at a point, 25 m from the centre is V kg/m. The value of V is :

  1. $-60 \, \mathrm{G}$
  2. $+2 \, \mathrm{G}$
  3. $-20 \, \mathrm{G}$
  4. $-4 \, \mathrm{G}$

Answer: (d)

Solution

The gravitational potential at point A is given by: $$V_A = \left[ -\frac{GM_1}{r} - \frac{GM_2}{R} \right]$$ Substituting the given values: $$= \left[ -\frac{50}{25}G - \frac{100}{50}G \right]$$ Simplifying, we get: $$= -4G$$

Question 42

Physics · Current Electricity · Single correct

For full scale deflection of total 50 divisions, 50 $\mathrm{mV}$ voltage is required in galvanometer. The resistance of galvanometer if its current sensitivity is 2 $\mathrm{div/mA}$ will be :

  1. 1$\Omega$
  2. 5$\Omega$
  3. 4$\Omega$
  4. 2$\Omega$

Answer: (d)

Solution

Given $$I_{max} = \frac{50}{2} = 25 \, mA$$ $$\mathbf{R} = \frac{V}{I} = \frac{50 \, mV}{25 \, mA} = 2 \, \Omega$$

Question 43

Physics · Dual Nature of Radiation and Matter · Single correct

A monochromatic neon lamp with wavelength of 670.5 nm illuminates a photo-sensitive material which has a stopping voltage of 0.48 V. What will be the stopping voltage if the source light is changed with another source of wavelength of 474.6 nm ?

  1. 0.96 V
  2. 1.25 V
  3. 0.24 V
  4. 1.5 V

Answer: (b)

Solution

$K E_{\max}=\dfrac{hc}{\lambda_i}-\phi$ or $eV_0=\dfrac{hc}{\lambda_i}-\phi$ when $\lambda_i=670.5\ \mathrm{nm};\qquad V_0=0.48$ when $\lambda_i=474.6\ \mathrm{nm};\qquad V_0=?$ $e(0.48)=\dfrac{1240}{670.5}-\phi$ So, $e(V_0)=\dfrac{1240}{474.6}-\phi$

Question 44

Physics · Physical World, Units and Measurements · Single correct

Match List-I with List-II. $$ \begin{array}{ll} \text{List-I} & \text{List-II} \\ \hline (a) \, R_H \text{ (Rydberg constant)} & (i) \, \mathrm{kgm^{-1} \, s^{-1}} \\ (b) \, h \text{ (Planck's constant)} & (ii) \, \mathrm{kgm^2 \, s^{-1}} \\ (c) \, \mu_B \text{ (Magnetic field energy density)} & (iii) \, \mathrm{m^{-1}} \\ (d) \, \eta \text{ (coefficient of viscosity)} & (iv) \, \mathrm{kgm^{-1} \, s^{-2}} \end{array} $$ Choose the most appropriate answer from the options given below:

  1. $(a) - (ii), (b) - (iii), (c)-(iv), (d)-(i)$
  2. $(a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)$
  3. $(a) - (iv), (b) - (ii), (c) - (i), (d) - (iii)$
  4. $(a) - (iii), (b) - (ii), (c)-(i), (d)-(iv)$

Answer: (b)

Solution

SI unit of Rydberg const. = $\mathrm{m^{-1}}$ SI unit of Planck's const. = $\mathrm{kg \, m^2 \, s^{-1}}$ SI unit of Magnetic field energy density = $\mathrm{kg \, m^{-1} \, s^{-2}}$ SI unit of coeff. of viscosity = $\mathrm{kg \, m^{-1} \, s^{-1}}$

Question 45

Physics · Physical World, Units and Measurements · Single correct

If force (F), length (L) and time (T) are taken as the fundamental quantities. Then what will be the dimension of density:

  1. $\left[\mathrm{FL}^{-4} \mathrm{T}^{2}\right]$
  2. $\left[\mathrm{FL}^{-3} \mathrm{T}^{2}\right]$
  3. $\left[\mathrm{FL}^{-5} \mathrm{T}^{2}\right]$
  4. $\left[\mathrm{FL}^{-3} \mathrm{T}^{3}\right]$

Answer: (a)

Solution

Density $= \left[ F^a L^b T^c \right]$ $\left[ ML^{-3} \right] = \left[ M^a L^a T^{-2a} L^b T^c \right]$ $\left[ M^1 L^{-3} \right] = \left[ M^a L^{a+b} T^{-2a+c} \right]$ $a = 1; \quad a + b = -3; \quad -2a + c = 0$ $1 + b = -3 \quad c = 2a$ $b = -4 \quad c = 2$ So, density $= \left[ F^1 L^{-4} T^2 \right]$

Question 46

Physics · Moving Charges and Magnetism · Single correct

A coaxial cable consists of an inner wire of radius 'a' surrounded by an outer shell of inner and outer radii 'b' and 'c' respectively. The inner wire carries an electric current $i_0$, which is distributed uniformly across cross-sectional area. The outer shell carries an equal current in opposite direction and distributed uniformly. What will be the ratio of the magnetic field at a distance $x$ from the axis when (i) $x < a$ and (ii) $a < x < b$ ?

  1. $\frac{x^2}{a^2}$
  2. $\frac{a^2}{x^2}$
  3. $\frac{x^2}{b^2-a^2}$
  4. $\frac{b^2-a^2}{x^2}$

Answer: (a)

Solution

When $x < a$: $$B_1(2 \pi x) = \mu_0 \left( \frac{i_0}{\pi a^2} \right) \pi x^2$$ $$B(2 \pi x) = \frac{\mu_0 i_0 a^2}{a^2}$$ $$B_1 = \frac{\mu_0 i_0 x}{2 \pi a^2}$$ When $a < x < b$: $$B_2(2 \pi x) = \mu_0 i_0$$ $$B_2 = \frac{\mu_0 i_0}{2 \pi x}$$ $$\frac{B_1}{B_2} = \frac{\mu_0 i_0 \frac{x}{2 \pi a^2}}{\frac{\mu_0 i_0}{2 \pi x}} = \frac{x^2}{a^2}$$

Question 47

Physics · Work, Energy and Power · Single correct

The height of Victoria Falls is $63\,\mathrm{m}$. What is the difference in temperature of water at the top and at the bottom of the fall? [Given $1\,\mathrm{cal}=4.2\,\mathrm{J}$ and the specific heat capacity of water $=1\,\mathrm{cal\,g^{-1}\,^\circ C^{-1}}$]

  1. $0.147^\circ\mathrm{C}$
  2. $14.76^\circ\mathrm{C}$
  3. $1.476^\circ\mathrm{C}$
  4. $0.014^\circ\mathrm{C}$

Answer: (a)

Solution

Change in P.E. = Heat energy $$mgh = mS \Delta T$$ $$\Delta T = \frac{gh}{S}$$ $$= \frac{10 \times 63}{4200 \, \mathrm{J/kg}^\circ \mathrm{C}}$$ $$= 0.147^\circ \mathrm{C}$$

Question 48

Physics · Motion in a Plane · Single correct

A player kicks a football with an initial speed of $25 \, \mathrm{ms^{-1}}$ at an angle of $45^\circ$ from the ground. What are the maximum height and the time taken by the football to reach at the highest point during motion ? (Take $g = 10 \, \mathrm{ms^{-2}}$ )

  1. $h_{max} = 10 \, \mathrm{m}$ $T = 2.5 \, \mathrm{s}$
  2. $h_{max} = 15.625 \, \mathrm{m}$ $T = 3.54 \, \mathrm{s}$
  3. $h_{max} = 15.625 \, \mathrm{m}$ $T = 1.77 \, \mathrm{s}$
  4. $h_{max} = 3.54 \, \mathrm{m}$ $T = 0.125 \, \mathrm{s}$

Answer: (c)

Solution

Given $$H = \frac{U^2 \sin^2 \theta}{2g}$$ Substituting the values, $$= \frac{(25)^2 \cdot (\sin 45)^2}{2 \times 10}$$ $$= 15.625 \, \mathrm{m}$$ For time, $$T = \frac{U \sin \theta}{g}$$ Substituting the values, $$= \frac{25 \times \sin 45^\circ}{10}$$ $$= 2.5 \times 0.7$$ $$= 1.77 \, \mathrm{s}$$

Question 49

Physics · Wave Optics · Single correct

The light waves from two coherent sources have same intensity $I_1 = I_2 = I_0$. In interference pattern the intensity of light at minima is zero. What will be the intensity of light at maxima?

  1. $I_0$
  2. $2I_0$
  3. $5I_0$
  4. $4I_0$

Answer: (d)

Solution

Given $$I_{max} = \left( \sqrt{I_1} + \sqrt{I_2} \right)^2$$ which simplifies to $$= 4I_0$$

Question 50

Physics · Electric Charges and Fields · Single correct

Figure shows a rod AB, which is bent in a $120^\circ$ circular arc of radius $R$. A charge $(-Q)$ is uniformly distributed over rod AB. What is the electric field $\vec{E}$ at the centre of curvature $O$ ?

  1. $\frac{3\sqrt{3}Q}{8\pi\varepsilon_0 R^2} \hat{i}$
  2. $\frac{3\sqrt{3}Q}{8\pi\varepsilon_0 R^2} \hat{i}$
  3. $\frac{3\sqrt{3}Q}{16\pi\varepsilon_0 R^2} \hat{i}$
  4. $\frac{3\sqrt{3}Q}{8\pi\varepsilon_0 R^2} (-\hat{i})$

Answer: (b)

Solution

Given $\varepsilon = \frac{2k\lambda}{R} \sin\left(\frac{\theta}{2}\right) \left(-\hat{i}\right)$. $\lambda = \left(\frac{-Q}{R\theta}\right) = \left(\frac{-Q}{R \cdot \frac{2\pi}{3}}\right)$. $\lambda = \frac{-3Q}{2\pi R}$. $\varepsilon = \frac{2k}{R} \cdot \frac{-3Q}{2\pi R} \cdot \sin(60^\circ) \left(-\hat{i}\right)$. $\varepsilon = \frac{3\sqrt{3}Q}{8\pi^2 \varepsilon_0 R^2} \left(+\hat{i}\right)$.

Question 51

Physics · Thermodynamics · Numerical

A heat engine operates between a cold reservoir at temperature $T_2 = 400 \, \mathrm{K}$ and a hot reservoir at temperature $T_1$. It takes $300 \, \mathrm{J}$ of heat from the hot reservoir and delivers $240 \, \mathrm{J}$ of heat to the cold reservoir in a cycle. The minimum temperature of the hot reservoir has to be _____$\mathrm{K}$.

Answer: 500

Solution

Question 52

Physics · Oscillations · Numerical

Two simple harmonic motion, are represented by the equations $y_1 = 10 \sin \left( 3 \pi t + \frac{\pi}{3} \right)$ $y_2 = 5 (\sin 3 \pi t + \sqrt{3} \cos 3 \pi t)$ Ratio of amplitude of $y_1$ to $y_2 = x : 1$. The value of $x$ is .......

Answer: 1

Solution

Given $$y_1 = 10 \sin \left( 3\pi t + \frac{\pi}{3} \right) \Rightarrow Amplitude = 10$$ $$y_2 = 5 (\sin 3\pi t + \sqrt{3} \cos 3\pi t)$$ $$y_2 = 10 \left( \frac{1}{2} \sin 3\pi t + \frac{\sqrt{3}}{2} \cos 3\pi t \right)$$ $$y_2 = 10 \left( \cos \frac{\pi}{3} \sin 3\pi t + \sin \frac{\pi}{3} \cos 3\pi t \right)$$ $$y_2 = 10 \sin \left( 3\pi t + \frac{\pi}{3} \right) \Rightarrow Amplitude = 10$$ So ratio of amplitudes = $\frac{10}{10}$ = 1

Question 53

Physics · Atoms · Numerical

X different wavelengths may be observed in the spectrum from a hydrogen sample if the atoms are exited to states with principal quantum number $n = 6$? The value of $X$ is

Answer: 15

Solution

Number of different wavelengths is given by the formula: $$\frac{n(n-1)}{2}$$ Substituting the values, we have: $$\frac{6 \times (6 - 1)}{2} = \frac{6 \times 5}{2} = 15$$

Question 54

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

A zener diode of power rating 2 W is to be used as a voltage regulator. If the zener diode has a breakdown of 10 V and it has to regulate voltage fluctuated between 6 V and 14 V, the value of $R_s$ for safe operation should be ____ $\Omega$

Answer: 20

Solution

When unregulated voltage is 14 V voltage across zener diode must be 10 V So potential difference across resistor $\Delta V_{R_s} = 4$ V and $P_{\text{zener}} = 2$ W $VI = 2$ $I = \dfrac{2}{10} = 0.2\,\text{A}$ $\Delta V_{R_s} = IR_s$ $4 = 0.2R_s \Rightarrow R_s = \dfrac{40}{2} = 20\,\Omega$

Question 55

Physics · Mechanical Properties of Solids · Numerical

Wires $W_1$ and $W_2$ are made of same material having the breaking stress of $1.25 \times 10^9 \, \mathrm{N/m^2}$. $W_1$ and $W_2$ have cross-sectional area of $8 \times 10^{-7} \, \mathrm{m^2}$ and $4 \times 10^{-7} \, \mathrm{m^2}$, respectively. Masses of $20 \, \mathrm{kg}$ and $10 \, \mathrm{kg}$ hang from them as shown in the figure. The maximum mass that can be placed in the pan without breaking the wires is _____ $\mathrm{kg}$. (Use $g = 10 \, \mathrm{m/s^2}$)

Answer: 40

Solution

$B.S_1=\frac{T_{\max}}{8\times10^{-7}}$ $\Rightarrow T_{1\max}=8\times1.25\times100$ $=1000\,\mathrm{N}$ $B.S_2=\frac{T_{2\max}}{4\times10^{-7}}$ $\Rightarrow T_{2\max}=4\times1.25\times100$ $=500\,\mathrm{N}$ $m=\frac{500-100}{10}$ $=40\,\mathrm{kg}$

Question 56

Physics · System of Particles and Rotational Motion · Numerical

A bullet of 10 g, moving with velocity $v$, collides head-on with the stationary bob of a pendulum and recoils with velocity $100 \, \mathrm{m/s}$. The length of the pendulum is $0.5 \, \mathrm{m}$ and mass of the bob is $1 \, \mathrm{kg}$. The minimum value of $v = \mathrm{m/s}$ so that the pendulum describes a circle. (Assume the string to be inextensible and $g = 10 \, \mathrm{m/s^2}$)

Answer: 400

Solution

Given $V' = \sqrt{5gR} = \sqrt{5 \times 10 \times 0.5}$. $V' = 5 \, \mathrm{m/s}$. $m_1 \, V = m_2 \times 5 - m_1 \times 100$. $$\frac{10}{1000} \times V = 5 - \frac{10}{1000} \times 100$$ $V = 400 \, \mathrm{m/s}$.

Question 57

Physics · Alternating Current · Numerical

An ac circuit has an inductor and a resistor of resistance $R$ in series, such that $X_L = 3R$. Now, a capacitor is added in series such that $X_C = 2R$. The ratio of new power factor with the old power factor of the circuit is $\sqrt{5} : x$. The value of $x$ is

Answer: 1

Solution

Given $\cos \phi = \frac{R}{\sqrt{R^2 + 3R^2}}$ and $\cos \phi' = \frac{R}{\sqrt{R^2 + R^2}}$. This simplifies to $\cos \phi = \frac{1}{\sqrt{10}} = \frac{1}{\sqrt{10}}$ and $\cos \phi' = \frac{1}{\sqrt{2}}$. Therefore, $\frac{\cos \phi'}{\cos \phi} = \frac{\sqrt{10}}{\sqrt{2}} = \frac{\sqrt{5}}{1}$. Thus, $x = 1$.

Question 58

Physics · Current Electricity · Numerical

The ratio of the equivalent resistance of the network (shown in figure) between the points a and b when switch is open and switch is closed is $x : 8$. The value of $x$ is

Answer: 9

Solution

Given $$R_{eq open} = \frac{3R}{2}$$ $$R_{eq closed} = 2 \times \frac{R \times 2R}{3R} = \frac{4R}{3}$$ Therefore, $$R_{eq open} \times R_{eq closed} = \frac{3R}{2} \times \frac{3}{4R} = \frac{9}{8}$$ Thus, $$x = 9$$

Question 59

Physics · Electromagnetic Waves · Numerical

A plane electromagnetic wave with frequency of $30\,\mathrm{MHz}$ travels in free space. At particular point in space and time, electric field is $6\,\mathrm{V/m}$. The magnetic field at this point will be $x \times 10^{-8}\,\mathrm{T}$. The value of $x$ is .....

Answer: 2

Solution

Given $|\mathbf{B}| = \frac{|\mathbf{E}|}{C} = \frac{6}{3 \times 10^8}$. This equals $2 \times 10^{-8} \, \mathrm{T}$. Therefore, $x = 2$.

Question 60

Physics · Waves · Numerical

A tuning fork is vibrating at $250 \, \mathrm{Hz}$. The length of the shortest closed organ pipe that will resonate with the tuning fork will be ..... $\mathrm{cm}$. (Take speed of sound in air as $340 \, \mathrm{ms}^{-1}$)

Answer: 34

Solution

Given $\frac{\lambda}{4} = \ell \Rightarrow \lambda = 4\ell$. The frequency $f = \frac{V}{\lambda} = \frac{V}{4\ell}$. Therefore, $$250 = \frac{340}{4\ell}$$ which implies $$\ell = \frac{34}{4 \times 25} = 0.34 \, \mathrm{m}$$ Thus, $\ell = 34 \, \mathrm{cm}$.

Chemistry

Question 61

Chemistry · The s-Block Elements · Single correct

Choose the correct statement from the following:

  1. The standard enthalpy of formation for alkali metal bromides becomes less negative on descending the group.
  2. The low solubility of CsI in water is due to its high lattice enthalpy.
  3. Among the alkali metal halides, LiF is least soluble in water.
  4. LiF has least negative standard enthalpy of formation among alkali metal fluorides.

Answer: (c)

Solution

(1) Standard enthalpy of formation for alkali metal bromides becomes more negative on descending down the group. (2) In case of CsI, lattice energy is less, but $\mathrm{Cs^+}$ is having less hydration enthalpy due to which it is less soluble in water. (3) For alkali metal fluorides, the solubility in water increases from lithium to caesium. LiF is least soluble in water. (4) Standard enthalpy of formation for LiF is most negative among alkali metal fluorides.

Question 62

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

The addition of dilute NaOH to $\mathrm{Cr}^{3+}$ salt solution will give:

  1. a solution of $[\mathrm{Cr(OH)}_4]^-$
  2. precipitate of $\mathrm{Cr}_2\mathrm{O}_3(\mathrm{H}_2\mathrm{O})_n$
  3. precipitate of $[\mathrm{Cr(OH)}_6]^{3-}$
  4. precipitate of $\mathrm{Cr(OH)}_3$

Answer: (b)

Solution

The reaction is given by: $$\mathrm{Cr^{3+} }+ NaOH \xrightarrow{dil.} Cr_2O_3 \cdot (H_2O)_n (precipitate)$$

Question 63

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

Given below are two statements : Statement I : Ethyl pent-4-yn-oate on reaction with $\mathrm{CH_3MgBr}$ gives a $3^\circ$-alcohol. Statement II : In this reaction one mole of ethyl pent-4-yn-oate utilizes two moles of $\mathrm{CH_3MgBr}$. In the light of the above statements, choose the most appropriate answer from the options given below :

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

Answer: (c)

Solution

Statement 1 is true. But it consumes 3 moles of Grignard Reagent (G R). So statement 2 is false.

Question 64

Chemistry · Environmental Chemistry · Single correct

In stratosphere most of the ozone formation is assisted by :

  1. cosmic rays.
  2. $\gamma$-rays.
  3. ultraviolet radiation.
  4. visible radiations.

Answer: (c)

Solution

Ozone in the stratosphere is a product of UV radiations acting on dioxygen ($\text{O}_2$) molecules. $\text{O}_2(\text{g}) \xrightarrow{\text{UV}} \text{O(g)} + \text{O(g)}$ $\text{O(g)} + \text{O}_2(\text{g}) \xrightleftharpoons{\text{UV}} \text{O}_3(\text{g})$

Question 65

Chemistry · Chemical Bonding and Molecular Structure · Single correct

The compound/s which will show significant intermolecular H-bonding is/are :

  1. only
  2. only
  3. and (b) only
  4. , (b) and (c)

Answer: (a)

Solution

Q5 (1) (a) Shows intra molecular H-bonding (b) Shows significant intermolecular H-bonding (c) It do not show intermolecular H-bonding due to steric hindrance.

Question 66

Chemistry · Chemistry in Everyday Life · Single correct

Which one of the following chemicals is responsible for the production of HCl in the stomach leading to irritation and pain?

Answer: (b)

Solution

Histamine stimulates the secretion of $\mathrm{HCl}$. Histamine structure

Question 67

Chemistry · The s-Block Elements · Single correct

The oxide that gives $\mathrm{H_2O_2}$ most readily on treatment with $\mathrm{H_2O}$ is:

  1. $\mathrm{PbO_2}$
  2. $\mathrm{Na_2O_2}$
  3. $\mathrm{SnO_2}$
  4. $\mathrm{BaO_2 \cdot 8H_2O}$

Answer: (b)

Solution

1. $\mathrm{PbO_2} + 2\mathrm{H_2O} \rightarrow \mathrm{Pb(OH)_4}$ 2. $\mathrm{Na_2O_2} + 2\mathrm{H_2O} \rightarrow 2\mathrm{NaOH} + \mathrm{H_2O_2}$ this reaction is possible at room temperature 3. $\mathrm{SnO_2} + 2\mathrm{H_2O} \rightarrow \mathrm{Sn(OH)_4}$ 4. Acidified $\mathrm{BaO_2.8H_2O}$ gives $\mathrm{H_2O_2}$ after evaporation.

Question 68

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

Which one of the following reactions will not yield propionic acid?

  1. $\mathrm{CH_3CH_2COCH_3 + OI^- / H_3O^+}$
  2. $\mathrm{CH_3CH_2CH_3 + KMnO_4(Heat), OH^- / H_3O^+}$
  3. $\mathrm{CH_3CH_2CCl_3 + OH^- / H_3O^+}$
  4. $\mathrm{CH_3CH_2CH_2Br + Mg, CO_2 \; dry \; ether / H_3O^+}$

Answer: (d)

Solution

All gives propanoic acid as product but option 4 gives butanoic as product. $$\mathrm{CH_3CH_2CH_2Br} \xrightarrow[Dry ether]{Mg} \mathrm{CH_3CH_2CH_2MgBr}$$ $$\mathrm{CH_3CH_2CH_2MgBr} \xrightarrow{CO_2} \mathrm{CH_3CH_2CH_2C(=O)OMgBr}$$ $$\mathrm{CH_3CH_2CH_2C(=O)OMgBr} \xrightarrow{H_3O^+} \mathrm{CH_3CH_2CH_2C(=O)OH}$$ Butanoic acid

Question 69

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

The correct order of ionic radii for the ions, $\mathrm{P}^{3-}$, $\mathrm{S}^{2-}$, $\mathrm{Ca}^{2+}$, $\mathrm{K}^{+}$, $\mathrm{Cl}^{-}$ is:

  1. $\mathrm{P}^{3-} > \mathrm{S}^{2-} > \mathrm{Cl}^{-} > \mathrm{K}^{+} > \mathrm{Ca}^{2+}$
  2. $\mathrm{Cl}^{-} > \mathrm{S}^{2-} > \mathrm{P}^{3-} > \mathrm{Ca}^{2+} > \mathrm{K}^{+}$
  3. $\mathrm{P}^{3-} > \mathrm{S}^{2-} > \mathrm{Cl}^{-} > \mathrm{Ca}^{2+} > \mathrm{K}^{+}$
  4. $\mathrm{K}^{+} > \mathrm{Ca}^{2+} > \mathrm{P}^{3-} > \mathrm{S}^{2-} > \mathrm{Cl}^{-}$

Answer: (a)

Solution

The correct order of ionic radii is $\mathrm{P^{3-} > S^{2-} > Cl^{-} > K^{+} > Ca^{2+}}$. All the given species are isoelectronic species. In isoelectronic species, size increases with increase of negative charge and size decreases with increase in positive charge.

Question 70

Chemistry · Amines · Single correct

Which one of the following is the major product of the given reaction?

Answer: (a)

Solution

The reaction begins with the addition of 2 equivalents of $\mathrm{CH_3MgBr}$ to the nitrile group $\mathrm{N\equiv C}$, forming a Grignard reagent intermediate. This intermediate undergoes a reaction with the ketone group, resulting in the formation of a tertiary alcohol. Upon treatment with $\mathrm{H_3O^+}$, the intermediate is protonated, leading to the formation of a stable alcohol. Finally, dehydration occurs in the presence of $\mathrm{H_2SO_4}$, resulting in the formation of the final product with a double bond.

Question 71

Chemistry · Hydrocarbons · Single correct

The major product (A) formed in the reaction given below is :

Answer: (b)

Solution

The reaction involves an elimination process (E2) where the base $\mathrm{CH_3O^-}$ in $\mathrm{CH_3OH}$ abstracts a proton from the $eta$-carbon. This leads to the formation of a double bond, resulting in the major product (A) which is an alkene: $$CH_3-CH_2-C \equiv CH_2$$ This is the major product due to the stability of the formed alkene.

Question 72

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

Which one of the following is used to remove most of plutonium from spent nuclear fuel?

  1. $\mathrm{ClF_3}$
  2. $\mathrm{O_2F_2}$
  3. $\mathrm{I_2O_5}$
  4. $\mathrm{BrO_3}$

Answer: (b)

Solution

$\mathrm{O_2F_2}$ oxidises plutonium to $\mathrm{PuF_6}$, and the reaction is used for removing plutonium as $\mathrm{PuF_6}$ from spent nuclear fuel.

Question 73

Chemistry · Surface Chemistry · Single correct

Lyophilic sols are more stable than lyophobic sols because :

  1. there is a strong electrostatic repulsion between the negatively charged colloidal particles.
  2. the colloidal particles have positive charge.
  3. the colloidal particles have no charge.
  4. the colloidal particles are solvated.

Answer: (d)

Solution

In the lyophilic colloids, the colloidal particles are extensively solvated.

Question 74

Chemistry · Haloalkanes and Haloarenes · Single correct

The major product of the following reaction, if it occurs by $S_N2$ mechanism is :

Answer: (d)

Solution

The reaction involves the deprotonation of phenol by a base to form the phenoxide ion. This ion then undergoes an $S_N^2$ reaction with the alkyl bromide to form the ether product.

Question 75

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

Potassium permanganate on heating at 513 K gives a product which is :

  1. paramagnetic and colourless
  2. diamagnetic and green
  3. diamagnetic and colourless
  4. paramagnetic and green

Answer: (d)

Solution

The reaction is given by: $$2\mathrm{KMnO_4} \xrightarrow{\Delta \, 200^\circ \mathrm{C}} \mathrm{K_2MnO_4} + \mathrm{MnO_2} + \mathrm{O_2}$$ In $\mathrm{K_2MnO_4}$, manganese oxidation state is $+6$ and hence it has one unpaired $e^-$.

Question 76

Chemistry · Biomolecules · Single correct

Which one of the following tests used for the identification of functional groups in organic compounds does not use copper reagent?

  1. Barfoed's test
  2. Seliwanoff's test
  3. Benedict's test
  4. Biuret test for peptide bond

Answer: (b)

Solution

In Seliwanoff's reagent, Cu is not present. In Barfoed, Biuret and in Benedict reagent Cu is present.

Question 77

Chemistry · Biomolecules · Single correct

Hydrolysis of sucrose gives :

  1. $\alpha$-D-(-)-Glucose and $\beta$-D-(-)-Fructose
  2. $\alpha$-D-(+)-Glucose and $\alpha$-D-(-)-Fructose
  3. $\alpha$-D-(-)-Glucose and $\alpha$-D-(+)-Fructose
  4. $\alpha$-D-(+)-Glucose and $\beta$-D-(-)-Fructose

Answer: (d)

Solution

Sucrose is formed by $\alpha - \mathrm{D}(+)$ Glucose $+ \beta - \mathrm{D}(-)$ Fructose. We obtain these monomers on hydrolysis.

Question 78

Chemistry · Co-ordination Compounds · Single correct

Match List – I with List – II Choose the most appropriate answer from the options given below :

  1. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
  2. (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
  3. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)
  4. (a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)

Answer: (a)

Solution

Name of ore/mineral (a) Calamine $\mathrm{ZnCO_3}$ (b) Malachite $\mathrm{CuCO_3 \cdot Cu(OH)_2}$ (c) Siderite $\mathrm{FeCO_3}$ (d) Sphalerite $\mathrm{ZnS}$

Question 79

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

Which one of the following is formed (mainly) when red phosphorus is heated in a sealed tube at 803 K?

  1. White phosphorus
  2. Yellow phosphorus
  3. $\beta$-Black phosphorus
  4. $\alpha$-Black phosphorus

Answer: (d)

Solution

When red phosphorus is heated in a sealed tube at $803 \, \mathrm{K}$, $\alpha$-black phosphorus is formed.

Question 80

Chemistry · Amines · Single correct

The correct structures of $A$ and $B$ formed in the following reactions are:

Answer: (d)

Solution

The reaction starts with the reduction of the nitro group to an amine using $\mathrm{H_2/Pd}$ in $\mathrm{C_2H_5OH}$, forming compound (A). Compound (A) is then reacted with acetic anhydride in a nucleophilic acyl substitution reaction to form an amide. The final product is compound (B), which is the major product.

Question 81

Chemistry · Chemical Kinetics and Nuclear Chemistry · Numerical

The first-order rate constant for the decomposition of $\mathrm{CaCO_3}$ at $700\,\mathrm{K}$ is $6.36 \times 10^{-3}\,\mathrm{s^{-1}}$ and the activation energy is $209\,\mathrm{kJ\,mol^{-1}}$. Its rate constant (in $\mathrm{s^{-1}}$) at $600\,\mathrm{K}$ is $x \times 10^{-6}$. The value of $x$ is \underline{\hspace{1cm}}. (Round off to the nearest integer.) Given: $R = 8.31\,\mathrm{J\,K^{-1}\,mol^{-1}}$, $\log(6.36 \times 10^{-3}) = -2.19$, $10^{-4.79} = 1.62 \times 10^{-5}$.

Answer: 16

Solution

Given $K_{700} = 6.36 \times 10^{-3} \, \mathrm{s^{-1}}$, $K_{600} = x \times 10^{-6} \, \mathrm{s^{-1}}$, $E_a = 209 \, \mathrm{kJ/mol}$. Applying: $$\log \left( \frac{K_{T_2}}{K_{T_1}} \right) = \frac{-E_a}{2.303R} \left( \frac{1}{T_2} - \frac{1}{T_1} \right)$$ $$\log \left( \frac{K_{700}}{K_{600}} \right) = \frac{-E_a}{2.303R} \left( \frac{1}{700} - \frac{1}{600} \right)$$ $$\log \left( \frac{6.36 \times 10^{-3}}{K_{600}} \right) = \frac{+209 \times 1000}{2.303 \times 8.31} \left( \frac{100}{700 \times 600} \right)$$ $$\log(6.36 \times 10^{-3}) - \log K_{600} = 2.6$$ $$\Rightarrow \log K_{600} = -2.19 - 2.6 = -4.79$$ $$\Rightarrow K_{600} = 10^{-4.79} = 1.62 \times 10^{-5}$$ $$= 16.2 \times 10^{-6}$$ $$= x \times 10^{-6}$$ $$\Rightarrow x = 16$$

Question 82

Chemistry · Co-ordination Compounds · Numerical

The number of optical isomers possible for $[\mathrm{Cr}(\mathrm{C}_2\mathrm{O}_4)_3]^{3-}$ is ____.

Answer: 2

Solution

The number of optical isomers for $[\mathrm{Cr}(\mathrm{C}_2\mathrm{O}_4)_3]^{3-}$ is two.

Question 83

Chemistry · States of Matter · Numerical

Two flasks I and II shown below are connected by a valve of negligible volume. When the valve is opened, the final pressure of the system in bar is $x \times 10^{-2}$. The value of $x$ is ____. (Integer answer) [Assume-Ideal gas; $1 \, bar = 10^5 \, Pa$; Molar mass of $\mathrm{N}_2 = 28.0 \, g mol^{-1}$; $R = 8.31 \, J mol^{-1} K^{-1}$]

Answer: 84

Solution

Applying; $(n_I + n_{II})_{initial} = (n_I + n_{II})_{final}$ Assuming the system attains a final temperature of $T$ (such that $300 < T < 60$) $$\Rightarrow \left( Heat lost by N_2 of container I \right) = \left( Heat gained by N_2 of container II \right)$$ $$\Rightarrow n_I C_m (300 - T) = n_{II} C_m (T - 60)$$ $$\Rightarrow \left( \frac{2.8}{28} \right) (300 - T) = \left( \frac{0.2}{28} \right) (T - 60)$$ $$\Rightarrow 14(300 - T) = T - 60$$ $$\Rightarrow \frac{(14 \times 300 + 60)}{15} = T$$ $$\Rightarrow T = 284 \, \mathrm{K} (final temperature)$$ If the final pressure $= P$ $$\Rightarrow (n_I + n_{II})_{final} = \left( \frac{3.0}{28} \right)$$ $$\Rightarrow \frac{P}{RT} (V_I + V_{II}) = \frac{3.0 \, \mathrm{gm}}{28 \, \mathrm{gm/mol}}$$ $$P = \left( \frac{3}{28} \, \mathrm{mol} \right) \times 8.31 \, \frac{\mathrm{J}}{\mathrm{mol} \, \mathrm{K}} \times \frac{284 \, \mathrm{K}}{3 \times 10^{-3} \, \mathrm{m}^3} \times 10^{-5} \, \frac{\mathrm{bar}}{\mathrm{Pa}}$$ $$\Rightarrow 0.84287 \, \mathrm{bar}$$ $$\Rightarrow 84.28 \times 10^{-2} \, \mathrm{bar}$$ $$\Rightarrow 84$$

Question 84

Chemistry · Some Basic Concepts of Chemistry · Numerical

100 $\mathrm{g}$ of propane is completely reacted with 1000 $\mathrm{g}$ of oxygen. The mole fraction of carbon dioxide in the resulting mixture is x $\times$ $10^{-2}$. The value of x is ____. (Nearest integer) [Atomic weight : $\mathrm{H}$ = 1.008; $\mathrm{C}$ = 12.00; $\mathrm{O}$ = 16.00 ]

Answer: 19

Solution

The reaction is given by $$\mathrm{C_3H_8_{(g)} + 5O_2_{(g)} \rightarrow 3CO_2_{(g)} + 4H_2O_{(\ell)}}$$ At $t = 0$, the moles are $2.27$ mole and $31.25$ mol. At $t = \infty$, the moles are $0$, $19.9$ mol, $6.81$ mol, and $9.08$ mol. The mole fraction of $\mathrm{CO_2}$ in the final reaction mixture (heterogeneous) is calculated as $$X_{\mathrm{CO_2}} = \frac{6.81}{19.9 + 6.81 + 9.08}$$ $$= 0.1902 = 19.02 \times 10^{-2}$$ Thus, the answer is $19$.

Question 85

Chemistry · Solutions · Numerical

40 g of glucose ( Molar mass = 180) is mixed with 200 mL of water. The freezing point of solution is ____ K (Nearest integer) [Given: $K_f = 1.86 \, \mathrm{K \, kg \, mol^{-1}}$; Density of water = $1.00 \, \mathrm{g \, cm^{-3}}$; Freezing point of water = $273.15 \, \mathrm{K}$]

Answer: 271

Solution

Given the molality, $$molality = \frac{\left( \frac{40}{180} \right) mol}{0.2 Kg} = \left( \frac{10}{9} \right) molal$$ implies $$\Delta T_f = T_f - T'_f = 1.86 \times \frac{10}{9}$$ implies $$T'_f = 273.15 - 1.86 \times \frac{10}{9}$$ $$= 271.08 K$$ $$\simeq 271 K (nearest-integer)$$

Question 86

Chemistry · Electrochemistry · Numerical

The resistance of a conductivity cell with cell constant $1.14 \, \mathrm{cm}^{-1}$, containing $0.001 \, \mathrm{M} \, \mathrm{KCl}$ at $298 \, \mathrm{K}$ is $1500 \, \Omega$. The molar conductivity of $0.001 \, \mathrm{M} \, \mathrm{KCl}$ solution at $298 \, \mathrm{K}$ in $\mathrm{S} \, \mathrm{cm}^2 \, \mathrm{mol}^{-1}$ is ____.

Answer: 760

Solution

Given $K = \frac{1}{R} \times \ell / A = \left( \left( \frac{1}{1500} \right) \times 1.14 \right) \, \mathrm{S \, cm^{-1}}$. Therefore, $\wedge_m = 1000 \times \frac{\left( \frac{1.14}{1500} \right)}{0.001} \, \mathrm{S \, cm^2 \, mol^{-1}} = 760 \, \mathrm{S \, cm^2 \, mol^{-1}}$. Thus, $\Rightarrow 760$.

Question 87

Chemistry · Structure of Atom · Numerical

The number of photons emitted by a monochromatic (single frequency) infrared range finder of power 1 mW and wavelength of 1000 nm, in 0.1 second is $x \times 10^{13}$. The value of $x$ is ____. (Nearest integer) $(h = 6.63 \times 10^{-34} \, \mathrm{Js}, \, c = 3.00 \times 10^8 \, \mathrm{ms}^{-1})$

Answer: 50

Solution

Energy emitted in 0.1 sec. $$= 0.1 \, sec. \times 10^{-3} \, \frac{\mathrm{J}}{\mathrm{s}}$$ $$= 10^{-4} \, \mathrm{J}$$ If 'n' photons of $\lambda = 1000 \, \mathrm{nm}$ are emitted, then; $$10^{-4} = n \times \frac{hc}{\lambda}$$ $$\Rightarrow 10^{-4} = \frac{n \times 6.63 \times 10^{-34} \times 3 \times 10^8}{1000 \times 10^{-9}}$$ $$\Rightarrow n = 5.02 \times 10^{14} = 50.2 \times 10^{13}$$ $$\Rightarrow 50 \; (nearest integer)$$

Question 88

Chemistry · Equilibrium · Numerical

When 5.1 g of solid $\mathrm{NH_4HS}$ is introduced into a two litre evacuated flask at $27^\circ \mathrm{C}$, 20$\%$ of the solid decomposes into gaseous ammonia and hydrogen sulphide. The $K_p$ for the reaction at $27^\circ \mathrm{C}$ is $x \times 10^{-2}$. The value of $x$ is ____. (Given $R = 0.082 L atm K^{-1} mol^{-1}$)

Answer: 6

Solution

Moles of $\mathrm{NH_4HS}$ initially taken $= \frac{5.1 \, \mathrm{g}}{51 \, \mathrm{g/mol}} = 0.1 \, \mathrm{mol}$. Volume of vessel $= 2 \, \ell$. $$\mathrm{NH_4HS_{(s)}} \rightleftharpoons \mathrm{NH_3}_{(g)} + \mathrm{H_2S}_{(g)}$$ At $t = 0$, $0.1 \, \mathrm{mol}$. At $t = \infty$, $0.1(1 - 0.2)$, $0.1 \times 0.2$, $0.1 \times 0.2$. Partial pressure of each component: $$P = \frac{nRT}{V} = \frac{0.1 \times 0.2 \times 0.082 \times 300}{2} = 0.246 \, \mathrm{atm}$$ $$\therefore \, K_P = P_{\mathrm{NH_3}} \times P_{\mathrm{H_2S}} = (0.246)^2 = 0.060516$$ $$= 6.05 \times 10^{-2}$$ $$\Rightarrow 6$$

Question 89

Chemistry · Chemical Bonding and Molecular Structure · Numerical

The number of species having non-pyramidal shape among the following is _____.

  1. $\mathrm{SO}_3$
  2. $\mathrm{NO}_3^-$
  3. $\mathrm{PCl}_3$
  4. $\mathrm{CO}_3^{2-}$

Answer: (c)

Solution

The first structure is $\mathrm{SO_3}$, which is trigonal planar. The second structure is $\mathrm{NO_3^-}$, which is also trigonal planar. The third structure is $\mathrm{CO_3^{2-}}$, which is trigonal planar. The fourth structure is $\mathrm{PCl_3}$, which is pyramidal. Hence non-pyramidal species are $\mathrm{SO_3}$, $\mathrm{NO_3^-}$ and $\mathrm{CO_3^{2-}}$.

Question 90

Chemistry · Thermodynamics · Numerical

Data given for the following reaction is as follows: The minimum temperature in K at which the reaction becomes spontaneous is ____. (Integer answer)

Answer: 964

Solution

Given $$T_{min} = \left( \frac{\Delta^0 H}{\Delta^0 S} \right)$$ $$\Delta^0 H_{rxn} = \left[ \Delta^0_f H(\mathrm{Fe}) + \Delta^0_f H(\mathrm{CO}) \right] - \left[ \Delta^0_f H(\mathrm{FeO}) + \Delta^0_f H(\mathrm{C(graphite)}) \right]$$ $$= [0 - 110.5] - [-266.3 + 0]$$ $$= 155.8 \, \mathrm{kJ/mol}$$ $$\Delta^0 S_{rxn} = \left[ \Delta^0 S(\mathrm{Fe}) + \Delta^0 S(\mathrm{CO}) \right] - \left[ \Delta^0 S(\mathrm{FeO}) + \Delta^0 S(\mathrm{C(graphite)}) \right]$$ $$= [27.28 + 197.6] - [57.49 + 5.74]$$ $$= 161.65 \, \mathrm{J/mol \cdot K}$$ $$T_{min} = \frac{155.8 \times 10^3 \, \mathrm{J/mol}}{161.65 \, \mathrm{J/mol \cdot K}} = 963.8 \, \mathrm{K}$$ $$\simeq 964 \, \mathrm{K} \text{ (nearest integer)}$$