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.
Register free to attempt this shift as a timed 180-minute test with instant scoring and chapter-wise analysis.
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:
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:
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:
$2 + \sqrt{3}$
$2 - \sqrt{3}$
$3 + 2\sqrt{2}$
$3 - 2\sqrt{2}$
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 :
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:
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 :
$x + 3 = 0$
$x + 1 = 0$
$x + 2 = 0$
$x + 4 = 0$
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:
$\vec{r} \cdot (\hat{j} - 3\hat{k}) + 6 = 0$
$\vec{r} \cdot (\hat{i} + 3\hat{k}) + 6 = 0$
$\vec{r} \cdot (\hat{i} - 3\hat{k}) + 6 = 0$
$\vec{r} \cdot (\hat{j} - 3\hat{k}) - 6 = 0$
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:
$y^5 - 2y - 2 = 0$
$2y^5 - 2y - 1 = 0$
$2y^5 - y^2 - 2 = 0$
$y^5 - y^2 - 1 = 0$
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:
$\frac{-2b}{b+1}$
$\frac{2b}{b+1}$
$\frac{2b^2}{b+1}$
$\frac{-2b^2}{b+1}$
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:
$\mathbb{R}$
(-$\infty$, -9) $\cup$ (-9, $\infty$)
[-9, -8)
(-$\infty$, -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:
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:
$\frac{a+b-\sqrt{a^2+b^2-ab}}{12}$
$\frac{a+b-\sqrt{a^2+b^2+ab}}{6}$
$\frac{a+b-\sqrt{a^2+b^2-ab}}{6}$
$\frac{a+b+\sqrt{a^2+b^2-ab}}{6}$
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:
$(p \land q) \Rightarrow (r \land q)$
$(q \land r) \Rightarrow (p \land q)$
$(p \land q) \Rightarrow (r \lor q)$
$(p \land r) \Rightarrow (p \land q)$
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:
16
25
49
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:
9
10
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:
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:
$x^2 + 2(a + 2b)x - b(a + b) = 0$
$x^2 + 2(a + 2b)x + a(a + b) = 0$
$x^2 - 2ax + b(a + b) = 0$
$x^2 - 2ax + a(a + b) = 0$
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:
$\frac{1}{2} e^2$
$2e$
$\frac{1}{2} \sqrt{e}$
$2e^2$
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:
If $\lim_{x \to \infty} \left( \sqrt{x^2 - x + 1 - ax} \right) = b$, then the ordered pair $(a, b)$ is:
$(1, \frac{1}{2})$
$(1, -\frac{1}{2})$
$(-1, \frac{1}{2})$
$(-1, -\frac{1}{2})$
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 .
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 .
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 .
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 .
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 .
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 .
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.
$\frac{1}{\mu_2 - \mu_1}$
$\mu_1 - \mu_2$
$\frac{1}{\mu_1 - \mu_2}$
$\mu_2 - \mu_1$
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 $g = 10 \, \mathrm{m/s^2}$)
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:
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.
4.18 m
2.94 m
2.45 m
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:
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
The colour coding on a carbon resistor is shown in the given figure. The resistance value of the given resistor is :
$(5700 \pm 285)\,\Omega$
$(7500 \pm 750)\,\Omega$
$(5700 \pm 375)\,\Omega$
$(7500 \pm 375)\,\Omega$
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 ?
37.8 m
605 m
75.6 m
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 $0^\circ \mathrm{C}$.
640 $\,$ $\mathrm{m/s}$
40 $\,$ $\mathrm{m/s}$
80 $\,$ $\mathrm{m/s}$
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 V
$2\pi V$
2 V
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 :
$-60 \, \mathrm{G}$
$+2 \, \mathrm{G}$
$-20 \, \mathrm{G}$
$-4 \, \mathrm{G}$
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 :
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 ?
0.96 V
1.25 V
0.24 V
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:
$(a) - (ii), (b) - (iii), (c)-(iv), (d)-(i)$
$(a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)$
$(a) - (iv), (b) - (ii), (c) - (i), (d) - (iii)$
$(a) - (iii), (b) - (ii), (c)-(i), (d)-(iv)$
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:
$\left[\mathrm{FL}^{-4} \mathrm{T}^{2}\right]$
$\left[\mathrm{FL}^{-3} \mathrm{T}^{2}\right]$
$\left[\mathrm{FL}^{-5} \mathrm{T}^{2}\right]$
$\left[\mathrm{FL}^{-3} \mathrm{T}^{3}\right]$
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) $a < x < b$ ?
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 $=1\,\mathrm{cal\,g^{-1}\,^\circ C^{-1}}$]
$0.147^\circ\mathrm{C}$
$14.76^\circ\mathrm{C}$
$1.476^\circ\mathrm{C}$
$0.014^\circ\mathrm{C}$
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 $g = 10 \, \mathrm{ms^{-2}}$ )
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?
$I_0$
$2I_0$
$5I_0$
$4I_0$
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 $O$ ?
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: $$\frac{6 \times (6 - 1)}{2} = \frac{6 \times 5}{2} = 15$$
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 $g = 10 \, \mathrm{m/s^2}$)
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 $g = 10 \, \mathrm{m/s^2}$)
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
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:
The standard enthalpy of formation for alkali metal bromides becomes less negative on descending the group.
The low solubility of CsI in water is due to its high lattice enthalpy.
Among the alkali metal halides, LiF is least soluble in water.
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:
a solution of $[\mathrm{Cr(OH)}_4]^-$
precipitate of $\mathrm{Cr}_2\mathrm{O}_3(\mathrm{H}_2\mathrm{O})_n$
precipitate of $[\mathrm{Cr(OH)}_6]^{3-}$
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 :
Both Statement I and Statement II are false.
Statement I is false but Statement II is true.
Statement I is true but Statement II is false.
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 :
cosmic rays.
$\gamma$-rays.
ultraviolet radiation.
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 :
only
only
and (b) only
, (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:
$\mathrm{PbO_2}$
$\mathrm{Na_2O_2}$
$\mathrm{SnO_2}$
$\mathrm{BaO_2 \cdot 8H_2O}$
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?
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?
$\mathrm{ClF_3}$
$\mathrm{O_2F_2}$
$\mathrm{I_2O_5}$
$\mathrm{BrO_3}$
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 :
there is a strong electrostatic repulsion between the negatively charged colloidal particles.
the colloidal particles have positive charge.
the colloidal particles have no charge.
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 :
paramagnetic and colourless
diamagnetic and green
diamagnetic and colourless
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?
Barfoed's test
Seliwanoff's test
Benedict's test
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 :
$\alpha$-D-(-)-Glucose and $\beta$-D-(-)-Fructose
$\alpha$-D-(+)-Glucose and $\alpha$-D-(-)-Fructose
$\alpha$-D-(-)-Glucose and $\alpha$-D-(+)-Fructose
$\alpha$-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 :
(a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
(a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
(a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)
(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?
White phosphorus
Yellow phosphorus
$\beta$-Black phosphorus
$\alpha$-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: $R = 8.31\,\mathrm{J\,K^{-1}\,mol^{-1}}$, $\log(6.36 \times 10^{-3}) = -2.19$, $10^{-4.79} = 1.62 \times 10^{-5}$.
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 = $273.15 \, \mathrm{K}$]
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 ____.
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 $R = 0.082 L atm K^{-1} mol^{-1}$)
Chemistry · Chemical Bonding and Molecular Structure · Numerical
The number of species having non-pyramidal shape among the following is _____.
$\mathrm{SO}_3$
$\mathrm{NO}_3^-$
$\mathrm{PCl}_3$
$\mathrm{CO}_3^{2-}$
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)