JEE Advanced 3 October 2021 Paper 1 question paper with solutions

JEE Advanced 3 October 2021 Paper 1: all 57 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 · Properties of Triangles · Single correct

Consider a triangle $\Delta$ whose two sides lie on the $x$-axis and the line $x + y + 1 = 0$. If the orthocenter of $\Delta$ is $(1, 1)$, then the equation of the circle passing through the vertices of the triangle $\Delta$ is

  1. $x^2 + y^2 - 3x + y = 0$
  2. $x^2 + y^2 + x + 3y = 0$
  3. $x^2 + y^2 + 2y - 1 = 0$
  4. $x^2 + y^2 + x + y = 0$

Answer: (b)

Solution

One of the vertices is the intersection of the x-axis and $x + y + 1 = 0$, which gives $A(-1, 0)$. Let vertex $B$ be $(\alpha, \alpha - 1)$. Line $AC \perp BH$ implies $\alpha = 1$, so $B(1, -2)$. Let vertex $C$ be $(\beta, 0)$. Line $AH \perp BC$. The product of slopes $m_{AH} \cdot m_{BC} = -1$. $$\frac{1}{2} \cdot \frac{2}{\beta - 1} = -1 \implies \beta = 0$$ The centroid of $\triangle ABC$ is $$\left(0, -\frac{2}{3}\right)$$ Now $G$ (centroid) divides the line joining the circumcenter $(O)$ and orthocenter $(H)$ in the ratio $1:2$. $$\begin{array}{ccc} (h, k) & (0, -\frac{2}{3}) & (1, 1) \\ O & 1 & G & 2 & H \end{array}$$ $$2h + 1 = 0 2k + 1 = -z$$ $$h = -\frac{1}{2} k = -\frac{3}{2}$$ Therefore, the circumcenter is $$\left(-\frac{1}{2}, -\frac{3}{2}\right)$$ The equation of the circumcircle is (passing through $C(0, 0)$) $$x^2 + y^2 + x + 3y = 0$$

Question 2

Maths · Applications of Integrals · Single correct

The area of the region \[ \left\{ (x,y):0\le x\le\frac{9}{4},\; 0\le y\le1,\; x\ge3y,\; x+y\ge2 \right\} \] is

  1. $\frac{11}{32}$
  2. $\frac{35}{96}$
  3. $\frac{37}{96}$
  4. $\frac{13}{32}$

Answer: (a)

Solution

Given $x + y - 2 = 0$. Points are $P \left( \frac{3}{2}, \frac{1}{2} \right)$, $Q(2, 0)$, $R \left( \frac{9}{4}, 0 \right)$, $S \left( \frac{9}{4}, \frac{3}{4} \right)$. The area is calculated as follows: $$Area = \frac{1}{2} \left| \begin{array}{ccc} \frac{3}{2} & \frac{1}{2} & 1 \\ 2 & 0 & 1 \\ \frac{9}{4} & 0 & 1 \\ \frac{9}{4} & \frac{3}{4} & 1 \end{array} \right|$$ $$= \frac{1}{2} \left| (0 - 1) + (0 - 0) + \left( \frac{27}{16} - 0 \right) + \left( \frac{9}{8} - \frac{9}{8} \right) \right| = \frac{11}{32}$$

Question 3

Maths · Probability · Single correct

Consider three sets $E_1 = \{1, 2, 3\}$, $F_1 = \{1, 3, 4\}$ and $G_1 = \{2, 3, 4, 5\}$. Two elements are chosen at random, without replacement, from the set $E_1$, and let $S_1$ denote the set of these chosen elements. Let $E_2 = E_1 - S_1$ and $F_2 = F_1 \cup S_1$. Now two elements are chosen at random, without replacement, from the set $F_2$ and let $S_2$ denote the set of these chosen elements. Let $G_2 = G_1 \cup S_2$. Finally, two elements are chosen at random, without replacement, from the set $G_2$ and let $S_3$ denote the set of these chosen elements. Let $E_3 = E_2 \cup S_3$. Given that $E_1 = E_3$, let $p$ be the conditional probability of the event $S_1 = \{1, 2\}$. Then the value of $p$ is

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

Answer: (a)

Solution

The probability is given by $$P = \frac{P(S_1 \cap (E_1 = E_3))}{P(E_1 = E_3)} = \frac{P(B_{1,2})}{P(B)}$$ where $$P(B) = P(B_{1,2}) + P(B_{1,3}) + P(B_{2,3})$$ If 1,2 are chosen at the start: $$P(B_{1,2}) = \frac{1}{3} \times \frac{1 \times \binom{3}{1}}{\binom{4}{2}} \times \frac{1}{\binom{5}{2}}$$ 1 is definitely chosen from $F_2$ and 1,2 are chosen from $G_2$. If 1,3 are chosen at the start: $$P(B_{1,3}) = \frac{1}{3} \times \frac{1 \times \binom{2}{1}}{\binom{3}{2}} \times \frac{1}{\binom{5}{2}}$$ 1 is definitely chosen from $F_2$ and 1,2 are chosen from $G_2$. If 2,3 are chosen at the start: $$P(B_{2,3}) = \frac{1}{3} \times \left[ \frac{\binom{3}{2} \times 1}{\binom{4}{2}} \times \frac{1}{\binom{4}{2}} + \frac{1 \times \binom{3}{1}}{\binom{4}{2}} \times \frac{1}{\binom{5}{2}} \right]$$ If 1 is not chosen from $F_2$ and if 1 is chosen from $F_2$. Finally, $$\frac{P(B_{1,2})}{P(B)} = \frac{1}{5}$$

Question 4

Maths · Complex Numbers and Quadratic Equations · Single correct

Let $\theta_1, \theta_2, ..., \theta_{10}$ be positive valued angles (in radian) such that $\theta_1 + \theta_2 + ... + \theta_{10} = 2\pi$. Define the complex numbers $z_1 = e^{i\theta_1}$, $z_k = z_{k-1} e^{i\theta_k}$ for $k = 2, 3, ..., 10$, where $i = \sqrt{-1}$. Consider the statements P and Q given below: P : $|z_2 - z_1| + |z_3 - z_2| + ... + |z_{10} - z_9| + |z_1 - z_{10}| \leq 2\pi$ Q : $|z_2^2 - z_1^2| + |z_3^2 - z_2^2| + ....+ |z_{10}^2 - z_9^2| + |z_1^2 - z_{10}^2| \leq 4\pi$ Then,

  1. P is TRUE and Q is FALSE
  2. Q is TRUE and P is FALSE
  3. both P and Q are TRUE
  4. both P and Q are FALSE

Answer: (c)

Solution

Given $|z_1| = |z_2| = \ldots |z_{10}| = 1$. The angle is given by $\frac{arc}{rad}$. $\theta_2 = arc(z_1 z_2) > (z_2 > z_1)$. For $P$: $|z_2 - z_1| + \ldots + |z_1 - z_{10}| \leq \theta_1 + \theta_2 + \ldots + \theta_{10}$. Therefore, $|z_2 - z_1| + \ldots + |z_1 - z_{10}| \leq 2\pi$ which means $P$ is true. $z_1^2 = e^{i2\theta_1}$, $z_k^2 = z_{k-1}^2 \cdot e^{i2\theta_k}$. Let $2\theta_k = \alpha_k$. Then $z_1^2 = e^{i\alpha_1}$, $z_k^2 = z_{k-1}^2 \cdot e^{i\alpha_k}$. $\alpha_1 + \alpha_2 + \ldots + \alpha_k = 4\pi$. In one similar sense, $|z_1^2 - z_2^2| + \ldots + |z_1^2 - z_{10}^2| \leq 4\pi$. $Q$ is also true.

Question 5

Maths · Basics Of Mathematics · Fill in the blank

Three numbers are chosen at random, one after another with replacement, from the set $S = \{1,2,3,\ldots,100\}$. Let $p_1$ be the probability that the maximum of chosen numbers is at least 81 and $p_2$ be the probability that the minimum of chosen numbers is at most 40. The value of $\frac{625}{4} p_1$ is _________.

Answer: 76.25

Solution

Let $p_1$ be the probability that the maximum of chosen numbers is at least 81. $p_1 = 1 -$ probability that the maximum of chosen numbers is at most 80. $$p_1 = 1 - \frac{80 \times 80 \times 80}{100 \times 100 \times 100} = 1 - \frac{64}{125}$$ $$p_1 = \frac{61}{125}$$ $$\frac{625 p_1}{4} = \frac{625}{4} \times \frac{61}{125} = \frac{305}{4} = 76.25$$ the value of $\frac{625 p_1}{4}$ is 76.25

Question 6

Maths · Permutations and Combinations · Numerical

Three numbers are chosen at random, one after another with replacement, from the set $S = \{1,2,3,\ldots,100\}$. Let $p_1$ be the probability that the maximum of chosen numbers is at least 81 and $p_2$ be the probability that the minimum of chosen numbers is at most 40. The value of $\frac{125}{4} p_2$ is

Answer: 24.5, 24.5, 24. 50, 24. 5

Solution

Given $p_2 =$ probability that minimum of chosen numbers is at most 40. $= 1 -$ probability that minimum of chosen numbers is at least 41. $$= 1 - \left( \frac{600}{100} \right)^3$$ $$= 1 - \frac{27}{125} = \frac{98}{125}$$ Therefore, $$\frac{125}{4} p_2 = \frac{125}{4} \times \frac{98}{125} = 24.50$$

Question 7

Maths · Determinants · Subjective

Let $\alpha$, $\beta$ and $\gamma$ be real numbers such that the system of linear equations $$x + 2y + 3z = \alpha$$ $$4x + 5y + 6z = \beta$$ $$7x + 8y + 9z = \gamma - 1$$ is consistent. Let $|M|$ represent the determinant of the matrix $$M = \begin{vmatrix} \alpha & 2 & \gamma \\ \beta & 1 & 0 \\ -1 & 0 & 1 \end{vmatrix}$$ Let $P$ be the plane containing all those $(\alpha, \beta, \gamma)$ for which the above system of linear equations is consistent, and $D$ be the square of the distance of the point $(0, 1, 0)$ from the plane $P$. The value of $|M|$ is:

Answer: 1

Question 8

Maths · Determinants · Fill in the blank

Let $\alpha, \beta$ and $\gamma$ be real numbers such that the system of linear equations \[ x + 2y + 3z = \alpha \] \[ 4x + 5y + 6z = \beta \] \[ 7x + 8y + 9z = \gamma - 1 \] is consistent. Let $|M|$ represent the determinant of the matrix \[ M = \begin{bmatrix} \alpha & 2 & \gamma \\ \beta & 1 & 0 \\ -1 & 0 & 1 \end{bmatrix} \] Let $P$ be the plane containing all those $(\alpha, \beta, \gamma)$ for which the above system of linear equations is consistent, and $D$ be the \textbf{square} of the distance of the point $(0, 1, 0)$ from the plane $P$. The value of $D$ is \underline{\hspace{2cm}}.

Answer: 1.5, 1.50, 1.5 units, 1.5 m, 1.5m, 1.5 metres, 1.5.0, 1.5e0

Solution

Given the equation $7x + 8y + 9z - (\gamma - 1) = A(4x + 5y + 6z - \beta) + B(x + 2y + 3z - \alpha)$. For $x$: $7 = 4A + B$. For $y$: $8 = 5A + 2B$. Solving these, we find $A = 2$, $B = -1$. The constant term: $-(\gamma - 1) = -A\beta - \alpha B \Rightarrow -(\gamma - 1) \equiv 2\beta + \alpha$. Thus, $\alpha - 2\beta + \gamma = 1$. The matrix $\mathbf{M}$ is given by: $$\mathbf{M} = \begin{pmatrix} \alpha & 2 & \gamma \\ \beta & 1 & 0 \\ -1 & 0 & 1 \end{pmatrix} = \alpha - 2\beta + \gamma = 1.$$ The plane $P$ is given by $x - 2y + z = 1$. The perpendicular distance is $\left| \frac{3}{\sqrt{6}} \right| = P \Rightarrow D = P^2 = \frac{9}{6} = 1.5$.

Question 9

Maths · Conic Sections · Fill in the blank

Consider the lines $L_1$ and $L_2$ defined by $L_1 : x\sqrt{2} + y - 1 = 0$ and $L_2 : x\sqrt{2} - y + 1 = 0$. For a fixed constant $\lambda$, let $C$ be the locus of a point $P$ such that the product of the distance of $P$ from $L_1$ and the distance of $P$ from $L_2$ is $\lambda^2$. The line $y = 2x + 1$ meets $C$ at two points $R$ and $S$, where the distance between $R$ and $S$ is $\sqrt{270}$. Let the perpendicular bisector of $RS$ meet $C$ at two distinct points $R'$ and $S'$. Let $D$ be the square of the distance between $R'$ and $S'$. The value of $\lambda^2$ is _________.

Answer: 9

Solution

Given $P(x, y)$, we have $$\left| \frac{\sqrt{2x + y - 1}}{\sqrt{3}} \right| \left| \frac{\sqrt{x - y + 1}}{\sqrt{3}} \right| = \lambda^2$$ $$\left| \frac{2x^2 - (y - 1)^2}{3} \right| = \lambda^2, \ C: \left| 2x^2 - (y - 1)^2 \right| = 3\lambda^2$$ The line is $y = 2x + 1$, and $RS = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}$, where $R(x_1, y_1)$ and $S(x_2, y_2)$. We have $y_1 = 2x_1 + 1$ and $y_2 = 2x_2 + 1$, which implies $(y_1 - y_2) = 2(x_1 - x_2)$. Therefore, $$RS = \sqrt{5(x_1 - x_2)^2} = \sqrt{5} |x_1 - x_2|$$ Solving the curve $C$ and the line $y = 2x + 1$, we get $$\left| 2x^2 - (2x)^2 \right| = 3\lambda^2 \implies x^2 = \frac{3\lambda^2}{2}$$ $$RS = \sqrt{5} \left| \frac{2\sqrt{3}\lambda}{\sqrt{2}} \right| = \sqrt{30} \lambda \implies 30\lambda^2 = 270 \implies \lambda^2 = 9$$

Question 10

Maths · Conic Sections · Subjective

Consider the lines $L_1$ and $L_2$ defined by $L_1: x\sqrt{2} + y - 1 = 0$ and $L_2: x\sqrt{2} - y + 1 = 0$. For a fixed constant $\lambda$, let $C$ be the locus of a point $P$ such that the product of the distance of $P$ from $L_1$ and the distance of $P$ from $L_2$ is $\lambda^2$. The line $y = 2x + 1$ meets $C$ at two points $R$ and $S$, where the distance between $R$ and $S$ is $\sqrt{270}$. Let the perpendicular bisector of $RS$ meet $C$ at two distinct points $R'$ and $S'$. Let $D$ be the square of the distance between $R'$ and $S'$. The value of $D$ is:

Answer: 77.14

Solution

Perpendicular bisector of RS. T = $\left$( $\frac{x_1 + x_2}{2}$, $\frac{y_1 + y_2}{2}$ $\right$) Here $x_1 + x_2 = 0$ T = (0, 1) Equation of R'S': (y - 1) = -$\frac{1}{2}$(x - 0) $\Rightarrow$ x + 2y = 2 R'(a_1, b_1) S'(a_2, b_2) D = (a_1 - a_2)^2 + (b_1 - b_2)^2 = 5(b_1 - b_2)^2 Solve $x + 2y = 2$ and $\left| 2x^2 - (y - 1)^2 \right| = 3 \lambda^2$ $\left$| 8(y - 1)^2 - (y - 1)^2 $\right$| = 3 $\lambda$^2 $\Rightarrow$ (y - 1)^2 = $\left$( $\frac{\sqrt{3 \lambda}}{\sqrt{7}}$ $\right$)^2 $y - 1 = \pm \frac{\sqrt{3 \lambda}}{\sqrt{7}} \Rightarrow b_1 = 1 + \frac{\sqrt{3 \lambda}}{\sqrt{7}}, b_2 = 1 - \frac{\sqrt{3 \lambda}}{\sqrt{17}}$ D = 5 $\left$( $\frac{2 \sqrt{3 \lambda}}{\sqrt{7}}$ $\right$)^2 = $\frac{5 \times 4 \times 3 \lambda^2}{7}$ = $\frac{5 \times 4 \times 27}{7}$ = 77.14

Question 11

Maths · Matrices · Multiple correct

For any $3 \times 3$ matrix M, let $|M|$ denote the determinant of M. Let $$E = \begin{bmatrix} 1 & 2 & 3 \\ 2 & 3 & 4 \\ 8 & 13 & 18 \end{bmatrix}, \ P = \begin{bmatrix} 1 & 0 \\ 0 & 1 \\ 0 & 0 \end{bmatrix} and F = \begin{bmatrix} 1 & 3 & 2 \\ 8 & 18 & 13 \\ 2 & 4 & 3 \end{bmatrix}$$ If Q is a nonsingular matrix of order $3 \times 3$, then which of the following statements is (are) TRUE?

  1. $F = PEP$ and $P^2 = \begin{bmatrix} 1 & 0 \\ 0 & 1 \\ 0 & 0 \end{bmatrix}$
  2. $|EQ + PFQ^{-1}| = |EQ| + |PFQ^{-1}|$
  3. $|(EF)^3| > |EF|^2$
  4. Sum of the diagonal entries of $P^{-1}EP + F$ is equal to the sum of diagonal entries of $E + P^{-1}FP$

Answer: (a), (b), (d)

Solution

PEP = $\begin{pmatrix}$ 1 & 0 & 0 $\\$ 0 & 0 & 1 $\\$ 0 & 1 & 0 $\end{pmatrix}$ $\begin{pmatrix}$ 1 & 2 & 3 $\\$ 8 & 13 & 18 $\\$ 2 & 3 & 4 $\end{pmatrix}$ $\begin{pmatrix}$ 1 & 0 & 0 $\\$ 0 & 0 & 1 $\\$ 0 & 1 & 0 $\end{pmatrix}$ = $\begin{pmatrix}$ 1 & 2 & 3 $\\$ 8 & 13 & 18 $\\$ 2 & 3 & 4 $\end{pmatrix}$ $\begin{pmatrix}$ 1 & 0 & 0 $\\$ 0 & 0 & 1 $\\$ 0 & 1 & 0 $\end{pmatrix}$ = $\begin{pmatrix}$ 1 & 0 & 0 $\\$ 0 & 1 & 0 $\\$ 0 & 0 & 1 $\end{pmatrix}$ P^2 = $\begin{pmatrix}$ 1 & 0 & 0 $\\$ 0 & 0 & 1 $\\$ 0 & 1 & 0 $\end{pmatrix}$ $\begin{pmatrix}$ 1 & 0 & 0 $\\$ 0 & 0 & 1 $\\$ 0 & 1 & 0 $\end{pmatrix}$ = $\begin{pmatrix}$ 1 & 0 & 0 $\\$ 0 & 1 & 0 $\\$ 0 & 0 & 1 $\end{pmatrix}$ (B) |EQ + PFQ^{-1}| = |EQ| + |PFQ^{-1}| |E| = 0 and |F| = 0 and |Q| $\neq$ 0 |EQ| = |E||Q| = 0 , PFQ^{-1} = $\frac{|P||F|}{|Q|}$ = 0 T = EQ + PFQ^{-1} TQ = EQ^2 + PF = EQ^2 + P^2EP = EQ^2 + EP = E(Q^2 + P) |TQ| = |E(Q^2 + P)| $\Rightarrow$ |T||Q| = |E||Q^2 + P| = 0 $\Rightarrow$ |T| = 0 (as |Q| $\neq$ 0) (C) (EF)^3 > |EF|^2 Here 0 > 0 (false) (D) as P^2 = I $\Rightarrow$ P^{-1} = P so P^{-1}FP = PFP = PEPP = E so E + P^{-1}FP = E + E = 2E P^{-1}EP + F $\Rightarrow$ PEP + F = 2PEP Tr(2PEP) = 2Tr(EP) = 2Tr(EPP) = 2Tr(E)

Question 12

Maths · Applications of Derivatives · Multiple correct

Let $f : \mathbb{R} \to \mathbb{R}$ be defined by $$f(x) = \frac{x^2 - 3x - 6}{x^2 + 2x + 4}.$$ Then which of the following statements is (are) TRUE?

  1. $f$ is decreasing in the interval $(-2, -1)$
  2. $f$ is increasing in the interval $(1, 2)$
  3. $f$ is onto
  4. Range of $f$ is $\left[ -\frac{3}{2}, 2 \right]$

Answer: (a), (b)

Solution

Given $\($ f(x) = $\frac{x^2 - 3x - 6}{x^2 + 2x + 4}$ $\)$. Differentiating, we have: $$ f'(x) = \frac{(x^2 + 2x + 4)(2x - 3) - (x^2 - 3x - 6)(2x + 2)}{(x^2 + 2x + 4)^2} $$ Simplifying, $$ f'(x) = \frac{5x(x + 4)}{(x^2 + 2x + 4)^2} $$ The sign of $\($ f'(x) $\)$ is analyzed as follows: $\($ f'(x) : + - + $\)$ at $\($ -4 $\)$ and $\($ 0 $\)$. Calculating specific values, $\($ f(-4) = $\frac{11}{6}$ $\)$, $\($ f(0) = -$\frac{3}{2}$ $\)$, and $\($ $\lim$_{x $\to$ $\pm$ $\infty$} f(x) = 1 $\)$. Thus, the range is $\($ $\left$[ -$\frac{3}{2}$, $\frac{11}{6}$ $\right$] $\)$, clearly $\($ f(x) $\)$ is into.

Question 13

Maths · Probability · Multiple correct

Let $\mathrm{E}$, $\mathrm{F}$ and $\mathrm{G}$ be three events having probabilities $\mathrm{P}$ ($\mathrm{E}$) = $\frac{1}{8}$, $\mathrm{P}$ ($\mathrm{F}$) = $\frac{1}{6}$ and $\mathrm{P}$ ($\mathrm{G}$) = $\frac{1}{4}$, and let $\mathrm{P}$ ($\mathrm{E}$ $\cap$ $\mathrm{F}$ $\cap$ $\mathrm{G}$) = $\frac{1}{10}$. For any event $\mathrm{H}$, if $\mathrm{H}^\mathrm{C}$ denotes its complement, then which of the following statements is(are) TRUE

  1. $\mathrm{P}$ ($\mathrm{E}$ $\cap$ $\mathrm{F}$ $\cap$ $\mathrm{G}$^{$\mathrm{C}$}) $\leq$ $\frac{1}{40}$
  2. $\mathrm{P}$ ($\mathrm{E}$^{$\mathrm{C}$} $\cap$ $\mathrm{F}$ $\cap$ $\mathrm{G}$) $\leq$ $\frac{1}{15}$
  3. $\mathrm{P}$ ($\mathrm{E}$ $\cup$ $\mathrm{F}$ $\cup$ $\mathrm{G}$) $\leq$ $\frac{13}{24}$
  4. $\mathrm{P}$ ($\mathrm{E}$^{$\mathrm{C}$} $\cap$ $\mathrm{F}$^{$\mathrm{C}$} $\cap$ $\mathrm{G}$^{$\mathrm{C}$}) $\leq$ $\frac{5}{12}$

Answer: (a), (b), (c)

Solution

P(E) = $\frac{1}{8}$; $\;$ P(F) = $\frac{1}{6}$; $\;$ P(G) = $\frac{1}{4}$; $\;$ P(E $\cap$ F $\cap$ G) = $\frac{1}{10}$ (C) $\;$ P(E $\cup$ F $\cup$ G) = P(E) + P(F) + P(G) - P(E $\cap$ F) - P(F $\cap$ G) - P(G $\cap$ E) + P(E $\cap$ F $\cap$ G) $$= \frac{1}{8} + \frac{1}{6} + \frac{1}{4} - \sum P(E \cap F) + \frac{1}{10}$$ $$= \frac{3 + 4 + 6}{24} + \frac{1}{10} - \sum P(E \cap F) = \frac{13}{24} + \frac{1}{10} - \sum P(E \cap F)$$ $$\Rightarrow P(E \cup F \cup G) \leq \frac{13}{24} [(C) is Correct]$$ (D) $\;$ P(E^C $\cap$ F^C $\cap$ G^C) = 1 - P(E $\cup$ F $\cup$ G) $\geq$ 1 - $\frac{13}{24}$ $$\Rightarrow P(E^C \cap F^C \cap G^C) \geq \frac{11}{24} [(D) is Incorrect]$$ (A) $\;$ P(E) = $\frac{1}{8}$ $\geq$ P(E $\cap$ F $\cap$ G^C) + P(E $\cap$ F $\cap$ G) $$\Rightarrow \frac{1}{8} \geq P(E \cap F \cap G^C) + \frac{1}{10} \Rightarrow \frac{1}{8} - \frac{1}{10} \geq P(E \cap F \cap G^C)$$ $$\Rightarrow \frac{1}{40} \geq P(E \cap F \cap G^C) [(A) is Correct]$$ (B) $\;$ P(F) = $\frac{1}{6}$ $\geq$ P(E^C $\cap$ F $\cap$ G) + P(E $\cap$ F $\cap$ G) $$\Rightarrow \frac{1}{6} - \frac{1}{10} \geq P(E^C \cap F \cap G)$$ $$\Rightarrow \frac{4}{60} \geq P(E^C \cap F \cap G)$$ $$\Rightarrow \frac{1}{15} \geq P(E^C \cap F \cap G) [(B) is Correct]$$

Question 14

Maths · Matrices · Multiple correct

For any 3 $\times$ 3 matrix M, let |M| denote the determinant of M. Let I be the 3 $\times$ 3 identity matrix. Let E and F be two 3 $\times$ 3 matrices such that (I - EF) is invertible. If G = (I - EF)^{-1}, then which of the following statements is (are) TRUE ?

  1. |FE| = |I - FE||FGE|
  2. |I - FE|(|I + FGE|) = I
  3. EFG = GEF
  4. (I - FE)(I - FGE) = I

Answer: (a), (b), (c)

Solution

Given $|I - EF| \neq 0$; $G = (I - EF)^{-1} \Rightarrow G^{-1} = I - EF$. Now, $G \cdot G^{-1} = I = G^{-1} G$. Therefore, $G (I - EF) = I = (I - EF) G$. This implies $G - GEF = I = G - EFG$. Hence, $GEF = EFG$ [C is Correct]. $(I - FE)(I + FGE) = I + FGE - FE - FEFGE = I + FGE - FE - F(G - I)E = I + FGE - FE - FGE + FE = I$ [(B) is Correct]. (So 'D' is Incorrect) We have $(I - FE)(I + FGE) = I$ .....(I) Now, $FE(I + FGE) = FE + FEFGE = FE + F(G - I)E = FE + FGE - FE = FGE$ Therefore, $|FE| |I + FGE| = |FGE|$. Thus, $|FE| \times \frac{1}{|I - FE|} = |FGE|$ (from (I)) Therefore, $|FE| = |I - FE| |FGE|$ (option (A) is correct).

Question 15

Maths · Inverse Trigonometric Functions · Multiple correct

For any positive integer $n$, let $S_n : (0, \infty) \to \mathbb{R}$ be defined by $$S_n(x) = \sum_{k=1}^{n} \cot^{-1}\left(\frac{1+k(k+1)x^2}{x}\right),$$ where for any $x \in \mathbb{R}$, $\cot^{-1}x \in (0,\pi)$ and $\tan^{-1}(x) \in \left(-\frac{\pi}{2}, \frac{\pi}{2}\right)$. Then which of the following statements is (are) TRUE ?

  1. $S_{10}(x) = \frac{\pi}{2} - \tan^{-1}\left(\frac{1+11x^2}{10x}\right), for all x > 0$
  2. $\lim_{n \to \infty} \cot\left(S_n(x)\right) = x, for all x > 0$
  3. The equation $S_3(x) = \frac{\pi}{4}$ has a root in $(0,\infty)$
  4. $\tan\left(S_n(x)\right) \leq \frac{1}{2}, for all n \geq 1 and x > 0$

Answer: (a)

Solution

Given $$S_n(x) = \sum_{k=1}^{n} \tan^{-1} \left( \frac{x}{1+kx(kx+x)} \right)$$ $$= \sum_{k=1}^{n} \tan^{-1} \left( \frac{(kx+x)-(kx)}{1+(kx+x)(kx)} \right)$$ $$S_n(x) = \tan^{-1}(nx+x) - \tan^{-1} x = \tan^{-1} \left( \frac{nx}{1+(n+1)x^2} \right)$$ (A) $S_{10}(x) = \tan^{-1} \frac{10x}{1+11x^2} = \frac{\pi}{2} - \tan^{-1} \left( \frac{1+11x^2}{10x} \right)$ $(x > 0)$ (B) $\lim_{n \to \infty} \cot(S_n(x)) = \lim_{n \to \infty} \frac{1}{x} \frac{n + \left(1 + \frac{1}{n}\right)x^2}{x} = x$ $(x > 0)$ (C) $S_3(x) = \tan^{-1} \frac{-3x}{1+4x^2} = \frac{\pi}{4} \Rightarrow 4x^2 - 3x + 1 = 0 \Rightarrow x \notin \mathbb{R}$ (D) $\tan(S_n(x)) = \frac{nx}{1+(n+1)x^2} ; \forall \ n \geq 1 ; x > 0$ We need to check the validity of $$\frac{nx}{1+(n+1)x^2} \leq \frac{1}{2} \forall \ n \geq 1 ; x > 0 ; n \in \mathbb{N}$$ $$\Rightarrow 2nx \leq (n+1)x^2 + 1$$ $$\Rightarrow (n+1)x^2 - 2nx + 1 \geq 0 \forall \ n \geq 1 ; x > 0 ; n \in \mathbb{N}$$ Discriminant of $y = (n+1)x^2 - 2nx + 1$ is $$D = 4n^2 - 4(n+1)$$ and $n \in \mathbb{N}$ $D 0$ $D > 0$ for $n \geq 2 \Rightarrow \exists$ some $x > 0$ for which $y 0 ; n \in \mathbb{N}$ is false.

Question 16

Maths · Complex Numbers and Quadratic Equations · Multiple correct

For any complex number $w = c + id$, let $\arg(w) \in (-\pi, \pi)$, where $i = \sqrt{-1}$. Let $\alpha$ and $\beta$ be real numbers such that for all complex numbers $z = x + iy$ satisfying $\arg\left(\frac{z + \alpha}{z + \beta}\right) = \frac{\pi}{4}$, the ordered pair $(x, y)$ lies on the circle $$x^2 + y^2 + 5x - 3y + 4 = 0.$$ Then which of the following statements is (are) TRUE?

  1. $\alpha = -1$
  2. $\alpha\beta = 4$
  3. $\alpha\beta = -4$
  4. $\beta = 4$

Answer: (b), (d)

Solution

The argument $\($ $\arg$ $\left$( $\frac{z + \alpha}{z + \beta}$ $\right$) = $\frac{\pi}{4}$ $\)$ implies $\($ z $\)$ is on arc and $\($(-$\alpha$, 0)$\)$ and $\($(-$\beta$, 0)$\)$ subtend $\($ $\frac{\pi}{4}$ $\)$ on $\($ z $\)$. And $\($ z $\)$ lies on $\($ x^2 + y^2 + 5x - 3y + 4 = 0 $\)$. So put $\($ y = 0 $\)$; $$ x^2 + 5x + 4 = 0 \implies x = -1 ; x = -4 $$ Now, $\($ $\arg$ $\left$( $\frac{z + \alpha}{z + \beta}$ $\right$) = $\frac{\pi}{4}$ $\)$ implies $\($ z + $\alpha$ = (z + $\beta$) $\cdot$ r $\cdot$ e^{i $\frac{\pi}{4}$} $\)$. So, $\($ z + $\beta$ = z + 4 $\implies$ $\beta$ = 4 $\)$ and $\($ z + $\alpha$ = z + 1 $\implies$ $\alpha$ = 1 $\)$.

Question 17

Maths · Complex Numbers and Quadratic Equations · Numerical

For $x \in \mathbb{R}$, then number of real roots of the equation $3x^2 - 4|x^2 - 1| + x - 1 = 0$ is _____.

Solution

Given $3x^2 + x - 1 = 4 \lvert x^2 - 1 \rvert$. If $x \in [-1, 1]$, then $3x^2 + x - 1 = -4x^2 + 4 \Rightarrow 7x^2 + x - 5 = 0$. Say $f(x) = 7x^2 + x - 5$. Then $f(1) = 3$; $f(-1) = 1$; $f(0) = -1$. [Two Roots] If $x \in (-\infty, -1] \cup [1, \infty)$, then $3x^2 + x - 1 = 4x^2 - 4 \Rightarrow x^2 - x - 3 = 0$. Say $g(x) = x^2 - x - 3$. Then $g(-1) = -1$; $g(1) = -3$. [Two Roots] So total 4 roots.

Question 18

Maths · Properties of Triangles · Fill in the blank

In a triangle ABC, let $AB = \sqrt{23}$, $BC = 3$ and $CA = 4$. Then the value of $\frac{\cot A + \cot C}{\cot B}$ is _____.

Answer: 2

Solution

Given $c = \sqrt{23}$, $a = 3$, $b = 4$. $$\cot A = \frac{\cos A}{\sin A} = \frac{b^2 + c^2 - a^2}{2bc \sin A}$$ $$= \frac{b^2 + c^2 - a^2}{2 \cdot 2 \Delta} \left\{ \Delta = \frac{1}{2} bc \sin A \right\}$$ $$\cot A = \frac{b^2 + c^2 - a^2}{4 \Delta}$$ Similarly, $\cot B = \frac{a^2 + c^2 - b^2}{4 \Delta}$ and $\cot C = \frac{a^2 + b^2 - c^2}{4 \Delta}$. Therefore, $$\cot A + \cot C = \frac{b^2 + c^2 - a^2 + a^2 + b^2 - c^2}{4 \Delta} = \frac{2b^2}{4 \Delta} = \frac{32}{16} = 2$$

Question 19

Maths · Vector Algebra · Numerical

Let $\vec{u}$, $\vec{v}$ and $\vec{w}$ be vectors in three-dimensional space, where $\vec{u}$ and $\vec{v}$ are unit vectors which are not perpendicular to each other and $\vec{u}$ $\cdot$ $\vec{w}$ = 1, $\vec{v}$ $\cdot$ $\vec{w}$ = 1, $\vec{w}$ $\cdot$ $\vec{w}$ = 4. If the volume of the parallelepiped, whose adjacent sides are represented by the vectors $\vec{u}$, $\vec{v}$ and $\vec{w}$, is $\sqrt{2}$, then the value of |3$\vec{u}$ + 5$\vec{v}$| is

Solution

Given, $|\mathbf{u}| = 1$; $|\mathbf{v}| = 1$; $\mathbf{u} \cdot \mathbf{v} \neq 0$; $\mathbf{u} \cdot \mathbf{w} = 1$; $\mathbf{v} \cdot \mathbf{w} = 1$; $$\mathbf{w} \cdot \mathbf{w} = |\mathbf{w}|^2 = 4 \implies |\mathbf{w}| = 2; \left[ \mathbf{u} \; \mathbf{v} \; \mathbf{w} \right] = \sqrt{2}$$ and $\left[ \mathbf{u} \; \mathbf{v} \; \mathbf{w} \right]^2 = \begin{vmatrix} \mathbf{v} \cdot \mathbf{u} & \mathbf{v} \cdot \mathbf{v} & \mathbf{v} \cdot \mathbf{w} \\ \mathbf{w} \cdot \mathbf{u} & \mathbf{w} \cdot \mathbf{v} & \mathbf{w} \cdot \mathbf{w} \end{vmatrix} = 2$ $$\begin{vmatrix} 1 & \mathbf{u} \cdot \mathbf{v} & 1 \\ \mathbf{u} \cdot \mathbf{v} & 1 & 1 \\ 1 & 1 & 4 \end{vmatrix} = 2$$ $$\implies \mathbf{u} \cdot \mathbf{v} = \frac{1}{2}$$ So, $|3\mathbf{u} + 5\mathbf{v}| = \sqrt{9|\mathbf{u}|^2 + 25|\mathbf{v}|^2 + 2 \cdot 3 \cdot 5 \mathbf{u} \cdot \mathbf{v}}$ $$= \sqrt{9 + 25 + 30 \left( \frac{1}{2} \right)} = \sqrt{49} = 7$$

Physics

Question 20

Physics · Physical World, Units and Measurements · Single correct

The smallest division on the main scale of a Vernier calipers is 0.1 cm. Ten divisions of the Vernier scale correspond to nine divisions of the main scale. The figure below on the left shows the reading of this calipers with no gap between its two jaws. The figure on the right shows the reading with a solid sphere held between the jaws. The correct diameter of the sphere is

  1. 3.07 $\mathrm{\ cm}$
  2. 3.11 $\mathrm{\ cm}$
  3. 3.15 $\mathrm{\ cm}$
  4. 3.17 $\mathrm{\ cm}$

Answer: (c)

Solution

Given 10 VSD = 9 MSD. $$1 VSD = \frac{9}{10} MSD$$ Least count = 1 MSD - 1 VSD $$= \left(1 - \frac{9}{10}\right) MSD$$ $$= 0.1 MSD$$ $$= 0.1 \times 0.1 cm$$ $$= 0.01 cm$$ As '0' of V.S. lie before '0' of M.S. Zero error $$= -[10 - 6] L.C.$$ $$= -4 \times 0.01 cm$$ $$= -0.04 cm$$ Reading $$= 3.1 cm + 1 \times LC$$ $$= 3.4 cm + 1 \times 0.01 cm$$ $$= 3.11 cm$$ True diameter = Reading - Zero error $$= 3.11 - (-0.04) cm = 3.15 cm$$

Question 21

Physics · Thermodynamics · Single correct

An ideal gas undergoes a four step cycle as shown in the $P - V$ diagram below. During this cycle, heat is absorbed by the gas in

  1. steps 1 and 2
  2. steps 1 and 3
  3. steps 1 and 4
  4. steps 2 and 4

Answer: (c)

Solution

Process 1 P = constant, Volume increases and temperature also increases ⇒ W = positive, ΔU = positive ⇒ Heat is positive and supplied to gas Process 2 V = constant, Pressure decrease ⇒ Temperature decreases $$W = \int pdV = 0$$ ΔT is negative and $$\Delta U = \frac{f}{2} nR \Delta T$$ ⇒ ΔU is negative ΔQ = ΔU + W ∴ ΔQ → Heat is negative and rejected by gas Process 3 P = constant, Volume decreases ⇒ Temperature also decreases W = PΔV = negative $$\Delta U = \frac{f}{2} nR \Delta T = negative$$ ΔQ = W + ΔU = negative Heat is negative and rejected by gas. Process 4 V = constant, Pressure increases $$W = \int pdV = 0$$ PV = nRT ⇒ Temperature increase ⇒ $$\Delta U = \frac{f}{2} nR \Delta T$$ is positive ΔQ = ΔU + W = positive Ans. (C) step 1 and step 4

Question 22

Physics · Ray Optics and Optical Instruments · Single correct

An extended object is placed at point O, 10 cm in front of a convex lens $L_1$ and a concave lens $L_2$ is placed 10 cm behind it, as shown in the figure. The radii of curvature of all the curved surfaces in both the lenses are 20 cm. The refractive index of both the lenses is 1.5. The total magnification of this lens system is

  1. 0.4
  2. 0.8
  3. 1.3
  4. 1.6

Answer: (b)

Solution

Focal length of convex lens ($f_1$) $$\frac{1}{f_1} = (\mu - 1) \left[ \frac{1}{R_1} - \frac{1}{R_2} \right]$$ $$= (1.5 - 1) \left[ \frac{1}{20} - \left( \frac{1}{-20} \right) \right]$$ $$\frac{1}{f_1} = \frac{1}{20}$$ Therefore, $f_1 = +20 \, \mathrm{cm}$ Focal length of concave lens ($f_2$) $$\frac{1}{f_2} = (\mu - 1) \left[ \frac{1}{R_1} - \frac{1}{R_2} \right]$$ $$\frac{1}{f_2} = (1.5 - 1) \left[ -\frac{1}{20} - \frac{1}{20} \right] = \frac{1}{-20}$$ Therefore, $f_2 = -20 \, \mathrm{cm}$ For lens 1 $$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$$ $$\Rightarrow v = -20 \, \mathrm{cm}$$ $$m_1 = \frac{v}{u} = \frac{-20}{-10} = 2$$ For lens 2 $$u = -30, \ f = -20, \ \frac{1}{v} - \frac{1}{u} = \frac{1}{f}$$ $$v = -12 \, \mathrm{cm}$$ $$m_2 = \frac{v}{u} = \frac{-12}{-30} = \frac{2}{5}$$ Net magnification $$m = m_1 m_2 = 2 \times \frac{2}{5} = \frac{4}{5} = 0.8$$

Question 23

Physics · Nuclei · Single correct

A heavy nucleus Q of half-life 20 minutes undergoes alpha-decay with probability of 60$\%$ and beta-decay with probability of 40$\%$. Initially, the number of Q nuclei is 1000. The number of alpha-decays of Q in the first one hour is

  1. 50
  2. 75
  3. 350
  4. 525

Answer: (d)

Solution

Out of 1000 nuclei of Q, 60$\%$ may go $\alpha$-decay. Therefore, 600 nuclei may have $\alpha$-decay. $$\lambda = \frac{\ln 2}{t_{1/2}} = \frac{\ln 2}{20}$$ $t = 1$ hour $= 60$ minutes. Using $$N = N_0 e^{-\lambda t}$$ $$= 600 \times e^{-\frac{\ln 2}{20} \times 60}$$ $$N = 75$$ Therefore, 75 nuclei are left after one hour. So, the number of nuclei decayed $$= 600 - 75 = 525$$

Question 24

Physics · Motion in a Plane · Subjective

A projectile is thrown from a point $O$ on the ground at an angle $45^\circ$ from the vertical and with a speed $5\sqrt{2} \, \mathrm{m/s}$. The projectile at the highest point of its trajectory splits into two equal parts. One part falls vertically down to the ground, $0.5 \, \mathrm{s}$ after the splitting. The other part, $t$ seconds after the splitting, falls to the ground at a distance $x$ meters from the point $O$. The acceleration due to gravity $g = 10 \, \mathrm{m/s^2}$. The value of t is ___.

Answer: 0.5

Question 25

Physics · Current Electricity · Fill in the blank

A projectile is thrown from a point $O$ on the ground at an angle $45^\circ$ from the vertical and with a speed $5\sqrt{2} \, \mathrm{m/s}$. The projectile at the highest point of its trajectory splits into two equal parts. One part falls vertically down to the ground, $0.5 \, \mathrm{s}$ after the splitting. The other part, $t$ seconds after the splitting, falls to the ground at a distance $x$ meters from the point $O$. The acceleration due to gravity $g = 10 \, \mathrm{m/s^2}$. The value of $x$ is ___.

Answer: 7.5

Solution

Range $R = \frac{2u_x u_y}{g} = \frac{2 \times 5 \times 5}{10} = 5 \, \mathrm{m}$. Time of flight $T = \frac{2u_y}{g} = \frac{2 \times 5}{10} = 1 \, \mathrm{sec}$. Therefore, time of motion of one part falling vertically downwards is $0.5 \, \mathrm{sec} = \frac{T}{2}$. Time of motion of another part, $t = \frac{T}{2} = 0.5 \, \mathrm{sec}$. From momentum conservation $\Rightarrow P_i = P_f$. $$2m \times 5 = m \times v$$ $$v = 10 \, \mathrm{m/s}$$ Displacement of other part in $0.5 \, \mathrm{sec}$ in horizontal direction $= v \frac{T}{2}$. $$= 10 \times 0.5 = 5 \, \mathrm{m} = R$$ Therefore, total distance of second part from point 'O' is, $x = \frac{3R}{2} = 3 \times \frac{5}{2}$. $$x = 7.5 \, \mathrm{m}$$ $t = 0.5 \, \mathrm{sec}$

Question 26

Physics · Electric Charges and Fields · Fill in the blank

In the circuit shown below, the switch $S$ is connected to position $P$ for a long time so that the charge on the capacitor becomes $q_1 \, \mu \mathrm{C}$. Then $S$ is switched to position $Q$. After a long time, the charge on the capacitor is $q_2 \, \mu \mathrm{C}$. The magnitude of $q_1$ is ___.

Answer: 1.33

Solution

Switch connected to position 'P'. $V_1 = i_1 \cdot 1 = 1 + 2 - 2i_1 = V_2$. $3i_1 = 1$ $i_1 = \frac{1}{3} \mathrm{A}$ $V_1 = 1 - i_1 = 1 - \frac{1}{3}$ $V_1 = \frac{2}{3} \mathrm{volt}$ Potential drop across capacitor $\Delta V = \frac{2}{3} \mathrm{volt}$ Charge on capacitor $q = C \Delta V$ $q_1 = 1 \mu \mathrm{F} \cdot \frac{2}{3} \mathrm{V}$ $q_1 = 1.33 \mu \mathrm{C}$ Switch at Position 'Q'. $V_1 = i_1 \cdot 1 = 2 - 2i_1 = V_2$ $3i_1 = 2$ $i_1 = \frac{2}{3} \mathrm{A}$ $V_1 = 2 - i_1 = 2 - \frac{2}{3}$ $V_1 = \frac{4}{3} \mathrm{volt}$ Potential difference across capacitor $\Delta V = \frac{2}{3} \mathrm{volt}$ Charge on capacitor $q = C \Delta V$ $q_2 = 1 \mu \mathrm{F} \cdot \frac{2}{3} \mathrm{V}$ $q_2 = 0.67 \mu \mathrm{C}$

Question 27

Physics · Electric Charges and Fields · Fill in the blank

In the circuit shown below, the switch $S$ is connected to position $P$ for a long time so that the charge on the capacitor becomes $q_1 \, \mu \mathrm{C}$. Then $S$ is switched to position $Q$. After a long time, the charge on the capacitor is $q_2 \, \mu \mathrm{C}$. The magnitude of $q_2$ is ___.

Answer: 0.67

Solution

Switch connected to position 'P'. $V_1 = i_1 \cdot 1 = 1 + 2 - 2i_1 = V_0$. $3i_1 = 1$ $i_1 = \frac{1}{3} \mathrm{A}$ $q_1 = i_1 \cdot 1 = \frac{1}{3} \mathrm{C}$ $V_0 - V_1 = \frac{1}{3} \mathrm{volt}$ Potential drop across capacitor $\Delta V = \frac{1}{3} \mathrm{volt}$. Charge on capacitor $q = C \Delta V$ $q_1 = 1 \cdot \frac{1}{3}$ $q_1 = 0.33 \mu \mathrm{C}$ Switch at Position 'Q'. $V_1 = i_1 \cdot 1 = 2 - 2i_1 = V_0$ $3i_1 = 2$ $i_1 = \frac{2}{3} \mathrm{A}$ $q_1 = i_1 \cdot 1 = \frac{2}{3} \mathrm{C}$ $V_0 - V_1 = \frac{2}{3} \mathrm{volt}$ Potential difference across capacitor $\Delta V = \frac{2}{3} \mathrm{volt}$. Charge on capacitor $q = C \Delta V$ $q_1 = 1 \cdot \frac{2}{3} = 0.67 \mu \mathrm{C}$

Question 28

Physics · Current Electricity · Fill in the blank

Two point charges $-Q$ and $+Q/\sqrt{3}$ are placed in the xy-plane at the origin $(0, 0)$ and a point $(2, 0)$, respectively, as shown in the figure. This results in an equipotential circle of radius $R$ and potential $V = 0$ in the xy-plane with its center at $(b, 0)$. All lengths are measured in meters. The value of $R$ is ___ meter.

Answer: 1.73

Solution

Let a point P on the circle. $$V_p = 0 = \frac{kQ}{r_1} + \frac{kQ/\sqrt{5}}{r_2}$$ $$\frac{kQ}{r_1} = \frac{kQ/\sqrt{5}}{r_2}$$ $$\frac{1}{\sqrt{x^2 + y^2}} = \frac{1}{\sqrt{5}\sqrt{(x-2)^2 + y^2}}$$ $$3(x^2 - 2x) + 3y^2 = x^2 + y^2$$ $$3(x^2 + 4 - 4x) - x^2 + 2y^2 = 0$$ $$2x^2 + 12 - 12x + 2y^2 = 0$$ $$x^2 + 6 - 6x + y^2 = 0$$ $$(x - 3)^2 + y^2 = \left(\sqrt{3}\right)^2$$ $$R = \sqrt{3} = 1.73$$ $$b = 3$$

Question 29

Physics · Physical World, Units and Measurements · Fill in the blank

Two point charges $-Q$ and $+Q/\sqrt{3}$ are placed in the xy-plane at the origin $(0, 0)$ and a point $(2, 0)$, respectively, as shown in the figure. This results in an equipotential circle of radius $R$ and potential $V = 0$ in the xy-plane with its center at $(b, 0)$. All lengths are measured in meters. The value of $b$ is ___ meter.

Answer: 3.0

Question 30

Physics · System of Particles and Rotational Motion · Multiple correct

A horizontal force $F$ is applied at the center of mass of a cylindrical object of mass $m$ and radius $R$, perpendicular to its axis as shown in the figure. The coefficient of friction between the object and the ground is $\mu$. The center of mass of the object has an acceleration $a$. The acceleration due to gravity is $g$. Given that the object rolls without slipping, which of the following statement(s) is(are) correct?

  1. For the same $F$, the value of $a$ does not depend on whether the cylinder is solid or hollow
  2. For a solid cylinder, the maximum possible value of $a$ is $2\mu g$
  3. The magnitude of the frictional force on the object due to the ground is always $\mu mg$
  4. For a thin-walled hollow cylinder, $a = \frac{F}{2m}$

Answer: (b), (d)

Solution

Given the forces and motion, we have the following equations: $$F - f = ma_c$$ $$fR = I_c \alpha$$ $$a_c - \alpha R = 0$$ Substituting, we get: $$F - \frac{I_c \alpha}{R} = ma_c$$ Solving for $a_c$: $$a_c = \frac{F}{\frac{I_c}{R^2} + m}$$ For the friction force $f$: $$f = \frac{I_c \alpha}{R} = \frac{I_c}{R^2} a_c = \frac{I_c}{R^2} \frac{F}{\left[ \frac{I_c}{R^2} + m \right]}$$ Thus, $$f = \frac{F}{\left[ m + \frac{I_c}{R^2} \right]}$$ For a thin-walled hollow cylinder, $$I_c = mR^2$$ Then, $$a_c = \frac{F}{2m}$$ Using the relation $$fR = I_c \alpha = \frac{I_c a_c}{R}$$ We have $$f = \frac{I_c a_c}{R^2} \leq \mu mg$$ Thus, $$a_c \leq \frac{\mu mg R^2}{I_c}$$ For a solid cylinder, $$I_c = \frac{mR^2}{2}$$ Then, $$a_c \leq 2 \mu g$$ The maximum acceleration $$(a_c)_{\max} = 2 \mu g$$

Question 31

Physics · Ray Optics and Optical Instruments · Multiple correct

A wide slab consisting of two media of refractive indices $n_1$ and $n_2$ is placed in air as shown in the figure. A ray of light is incident from medium $n_1$ to $n_2$ at an angle $\theta$, where $\sin \theta$ is slightly larger than $1/n_1$. Take refractive index of air as 1. Which of the following statement(s) is(are) correct?

  1. The light ray enters air if $n_2 = n_1$
  2. The light ray is finally reflected back into the medium of refractive index $n_1$ if $n_2 < n_1$
  3. The light ray is finally reflected back into the medium of refractive index $n_1$ if $n_2 > n_1$
  4. The light ray is reflected back into the medium of refractive index $n_1$ if $n_2 = 1$

Answer: (b), (c), (d)

Solution

Given $\sin \theta_0 = \frac{1}{n_1}$ (given). i.e. $\sin \theta_1 > \frac{1}{n_1}$. $n_1 \sin \theta_1 = n_1 \sin \theta_0$. $\sin \theta_1 = n \sin \theta_0$. $\sin \theta_2 = \frac{n \sin \theta_1}{n_2}$. If $n_1 = n_2$ then $\theta_2 = \theta_1$. $n_2 \sin \theta_2 = (1) \sin \theta_0$. $\sin \theta_2 = n_1 \sin \theta_0$. $\sin \theta_1 = n_1 \sin \theta_1$. $\sin \theta_1 = \frac{\sin \theta_2}{n_1} > \frac{1}{n_1}$. $\sin \theta_1 > 1$. $\theta_3 > 90^\circ$. This means ray cannot enter air. For $n_1 > n_2$: $\sin \theta_1 = \frac{n_2}{n_1} \sin \theta_2 > \frac{1}{n_1}$. $\sin \theta_1 > \frac{1}{n_2}$. For surface 2 - air interface $n_1 \sin \theta_0 = \sin \theta_1$. $\sin \theta_1 = \frac{\sin \theta_0}{n_2} > \frac{1}{n_2}$. $\theta_2 > 90^\circ$. It means ray is reflected back in medium-2. For surface 1 - surface 2 interface $n_1 \sin \theta_0 = n_1 \sin \theta_1$. $\sin \theta_c = \frac{n_1}{n_2}$. $\theta_c$: critical angle for ray to enter medium-1. $\theta_2 n_1$: $\frac{n_2}{n_1} \sin \theta_0 > \frac{n_2}{n_1}$. $\sin \theta_0 > \frac{1}{n_2}$. For surface 2 - air interface $n_2 \sin \theta_2 = \sin \theta_3$. $\sin \theta_2 = \frac{\sin \theta_0}{n_2} > \frac{1}{n_2}$. $\theta_2 > 90$. It means ray is reflected back in medium-2. $n_2 \sin \theta_2 = n_1 \sin \theta_1$. $\sin \theta_c = \frac{n_1}{n_2}$, $\theta_c$: critical angle. For ray to enter medium-1 $\theta_2 \frac{1}{n_1}$. $\sin \theta_2 > 1 = \theta_2 > 90^\circ$. Ray is reflected back in medium-

Question 32

Physics · System of Particles and Rotational Motion · Multiple correct

A particle of mass $M = 0.2 \, \mathrm{kg}$ is initially at rest in the $xy$-plane at a point $(x = -l, y = -h)$, where $l = 10 \, \mathrm{m}$ and $h = 1 \, \mathrm{m}$. The particle is accelerated at time $t = 0$ with a constant acceleration $a = 10 \, \mathrm{m/s^2}$ along the positive $x$-direction. Its angular momentum and torque with respect to the origin, in SI units, are represented by $\vec{L}$ and $\vec{\tau}$, respectively. $\hat{i}, \hat{j}$ and $\hat{k}$ are unit vectors along the positive $x$, $y$ and $z$-directions, respectively. If $\hat{k} = \hat{i} \times \hat{j}$ then which of the following statement(s) is(are) correct?

  1. The particle arrives at the point $(x = l, y = -h)$ at time $t = 2 \, \mathrm{s}$.
  2. $\vec{\tau} = 2 \hat{k}$ when the particle passes through the point $(x = l, y = -h)$
  3. $\vec{L} = 4 \hat{k}$ when the particle passes through the point $(x = l, y = -h)$
  4. $\vec{\tau} = \hat{k}$ when the particle passes through the point $(x = 0, y = -h)$

Answer: (a), (b), (c)

Solution

Given $\vec{r}_A = -\hat{j}$. $S = \frac{1}{2} a t^2$ $20 = \frac{1}{2} \times 10 \times t^2$ $t = 2 sec$ $\vec{\tau}_o = \vec{r} \times \vec{F}; \; \vec{r}_B = 10 \hat{i} - \hat{j}$ $\vec{F} = m \vec{a} = 0.2 \times 10 \hat{i} = 2 \hat{i}$ $\vec{\tau}_o = (10 \hat{i} - \hat{j}) \times (2 \hat{i})$ $\vec{\tau}_o = 2 \hat{k}$ $\vec{L}_o = \vec{r}_B \times \vec{p} = \vec{r}_B \times m \vec{v}$ $\vec{v} = \vec{a} t = 10 \hat{i} \times 2 = 20 \hat{i}$ $\vec{L}_o = (0.2) \left[ (10 \hat{i} - \hat{j}) \times 20 \hat{i} \right] = 4 \hat{k}$ At point $A(0, -1)$ $\vec{\tau}_o = \vec{r}_A \times \vec{F} = (-\hat{j}) \times 2 \hat{i} = 2 \hat{k}$

Question 33

Physics · Atoms · Multiple correct

Which of the following statement(s) is(are) correct about the spectrum of hydrogen atom?

  1. The ratio of the longest wavelength to the shortest wavelength in Balmer series is $9/5$
  2. There is an overlap between the wavelength ranges of Balmer and Paschen series.
  3. The wavelengths of Lyman series are given by $\left(1 + \frac{1}{m^2}\right) \lambda_0$, where $\lambda_0$ is the shortest wavelength of Lyman series and $m$ is an integer
  4. The wavelength ranges of Lyman and Balmer series do not overlap

Answer: (a), (d)

Solution

For A When the transition is from any level to $n = 2$, then photon emitted belong to Balmer series. Therefore, for longest wavelength, transition occurs from $n = 3$ to $n = 2$. $$\frac{hc}{\lambda_{\max}} = \mathrm{RCh} \left[ \frac{1}{2^2} - \frac{1}{3^2} \right]$$ and for shortest wavelength transition occurs from $n = \infty$ to $n = 2$ $$\frac{hc}{\lambda_{\min}} = \mathrm{RCh} \left[ \frac{1}{2^2} - \frac{1}{\infty^2} \right]$$ Thus, $$\frac{\lambda_{longest}}{\lambda_{shortest}} = \frac{9}{5}$$ For (B) $$\lambda_{longest} of Balmer = \frac{36}{5R}$$ $$\lambda_{shortest} of Paschen = \frac{9}{R}$$ Hence these wavelength don't overlap. For (C) For Lyman series, $$\frac{1}{\lambda} = \mathrm{R} \left[ 1 - \frac{1}{m^2} \right]$$ Also $$\frac{1}{\lambda_0} = \mathrm{R}$$ Thus, $$\frac{1}{\lambda} = \frac{1}{\lambda_0} \left[ 1 - \frac{1}{m^2} \right] \implies \lambda = \frac{\lambda_0}{1 - \frac{1}{m^2}}$$ For (D) $$\lambda_{longest} of Lyman = \frac{4}{3R}, \lambda_{shortest} of Balmer = \frac{4}{R}$$ Hence that wavelength don't overlap.

Question 34

Physics · Electromagnetic Induction · Multiple correct

A long straight wire carries a current, $I = 2$ ampere. A semi-circular conducting rod is placed beside it on two conducting parallel rails of negligible resistance. Both the rails are parallel to the wire. The wire, the rod and the rails lie in the same horizontal plane, as shown in the figure. Two ends of the semi-circular rod are at distances $1 \, \mathrm{cm}$ and $4 \, \mathrm{cm}$ from the wire. At time $t = 0$, the rod starts moving on the rails with a speed $v = 3.0 \, \mathrm{m/s}$ (see the figure). A resistor $R = 1.4 \, \Omega$ and a capacitor $C_0 = 5.0 \, \mu \mathrm{F}$ are connected in series between the rails. At time $t = 0$, $C_0$ is uncharged. Which of the following statement(s) is(are) correct? $[\mu_0 = 4 \pi \times 10^{-7} \, \mathrm{SI}$ units. Take $\ln 2 = 0.7$]

  1. Maximum current through $R$ is $1.2 \times 10^{-6}$ ampere
  2. Maximum current through $R$ is $3.8 \times 10^{-6}$ ampere
  3. Maximum charge on capacitor $C_0$ is $8.4 \times 10^{-12}$ coulomb
  4. Maximum charge on capacitor $C_0$ is $2.4 \times 10^{-12}$ coulomb

Answer: (a), (c)

Solution

EMF developed across the emf of semi-circular rod is given by $$ \int_1^4 \frac{\mu_0 i}{2 \pi r} \, drv = \frac{\mu_0 i V}{2 \pi} \ln 4 = \frac{\mu_0 i V}{\pi} \ln 2 $$ From given value, $$ E = \frac{4 \pi \times 10^{-7} \times 2 \times 3 \times 0.7}{\pi} = 24 \times 7 \times 10^{-8} $$ $$ i_{max} = \frac{E}{R} = \frac{24 \times 7 \times 10^{-8}}{1.4} = 1.2 \times 10^{-6} \, A $$ $$ Q_{max} = C_0 E = 24 \times 7 \times 10^{-8} \times 5 \times 10^{-6} = 8.4 \times 10^{-12} \, C $$

Question 35

Physics · Mechanical Properties of Fluids · Multiple correct

A cylindrical tube, with its base as shown in the figure, is filled with water. It is moving down with a constant acceleration $a$ along a fixed inclined plane with angle $\theta = 45^\circ$. $P_1$ and $P_2$ are pressures at points $1$ and $2$, respectively, located at the base of the tube. Let $\beta = (P_1 - P_2)/(\rho g d)$, where $\rho$ is density of water, $d$ is the inner diameter of the tube and $g$ is the acceleration due to gravity. Which of the following statement(s) is(are) correct?

  1. $\beta = 0$ when $a = g/\sqrt{2}$
  2. $\beta > 0$ when $a = g/\sqrt{2}$
  3. $\beta = \frac{\sqrt{2} - 1}{\sqrt{2}}$ when $a = g/2$
  4. $\beta = \frac{1}{\sqrt{2}}$ when $a = g/2$

Answer: (a), (c)

Solution

Therefore, $P_1 - P_3 = \rho \left( g - \frac{a}{\sqrt{2}} \right) d$. $P_2 - P_3 = \rho \frac{a}{\sqrt{2}} d$. Therefore, $P_1 - P_2 = \rho d \left[ g - \frac{2a}{\sqrt{2}} \right]$. Therefore, $\frac{P_1 - P_2}{\rho g d} = \left[ 1 - \sqrt{2} \frac{a}{g} \right] = \beta$. Therefore, if $\beta = 0$, $a = \frac{g}{\sqrt{2}} \ldots (A)$. $\beta = \frac{\sqrt{2} - 1}{2}$, $a = \frac{g}{2} \ldots (C)$.

Question 36

Physics · Moving Charges and Magnetism · Numerical

An $\alpha$-particle (mass 4 amu) and a singly charged sulfur ion (mass 32 amu) are initially at rest. They are accelerated through a potential $V$ and then allowed to pass into a region of uniform magnetic field which is normal to the velocities of the particles. Within this region, the $\alpha$-particle and the sulfur ion move in circular orbits of radii $r_{\alpha}$ and $r_{s}$, respectively. The ratio $\left( \frac{r_{s}}{r_{\alpha}} \right)$ is ___.

Answer: 4

Solution

The radius is given by the equation $$r = \frac{mv}{qB} = \frac{\sqrt{2mqV}}{qB}$$. The kinetic energy is expressed as $$\frac{P^2}{2m} = K.E = qV$$. The ratio of radii is calculated as $$\frac{r_s}{r_\alpha} = \sqrt{\frac{32}{1} \times \frac{2}{4}} = 4$$. Therefore, $$\frac{r_s}{r} = 4$$.

Question 37

Physics · System of Particles and Rotational Motion · Numerical

A thin rod of mass $M$ and length $a$ is free to rotate in horizontal plane about a fixed vertical axis passing through point $O$. A thin circular disc of mass $M$ and of radius $a/4$ is pivoted on this rod with its center at a distance $a/4$ from the free end so that it can rotate freely about its vertical axis, as shown in the figure. Assume that both the rod and the disc have uniform density and they remain horizontal during the motion. An outside stationary observer finds the rod rotating with an angular velocity $\Omega$ and the disc rotating about its vertical axis with angular velocity $4\Omega$. The total angular momentum of the system about the point $O$ is $$\left( \frac{Ma^2\Omega}{48} \right) n$$. The value of $n$ is___.

Answer: 49

Solution

Given $$L = \frac{Ma^2}{3} \Omega + M \left( \frac{3a}{4} \right)^2 \Omega + \frac{M \left( \frac{a}{4} \right)^2 4 \Omega}{2}$$ Then $$L = \frac{49}{48} Ma^2 \Omega$$ Finally, $$n = 49$$

Question 38

Physics · Thermal Properties of Matter · Numerical

A small object is placed at the center of a large evacuated hollow spherical container. Assume that the container is maintained at 0 $\,$ $\mathrm{K}$. At time $t = 0$, the temperature of the object is 200 $\,$ $\mathrm{K}$. The temperature of the object becomes 100 $\,$ $\mathrm{K}$$ at $t = t_1$ and 50 \, \mathrm{K}$ at $t = t_2$. Assume the object and the container to be ideal black bodies. The heat capacity of the object does not depend on temperature. The ratio $(t_2/t_1)$ is____.

Answer: 9

Solution

Given $\sigma A T^4 = -ms \frac{dT}{dt}$. $$\int_{200}^{100} \frac{dT}{T^4} = \int_{0}^{t_1} k \, dt$$ $$\left. \frac{1}{3T^3} \right|_{200}^{100} = kt_1$$ $$\frac{1}{3} \left( \frac{1}{100^3} - \frac{1}{200^3} \right) = kt_1$$ $$\left. \frac{1}{3T^3} \right|_{200}^{50} = kt_2$$ $$\frac{1}{3} \left( \frac{1}{50^3} - \frac{1}{200^3} \right) = kt_2$$ $$\frac{t_2}{t_1} = \left( \frac{200^3 - 50^3}{200^3 - 100^3} \right) \left( \frac{100^3}{50^3} \right) = 9$$

Chemistry

Question 39

Chemistry · Hydrocarbons · Single correct

The major product formed in the following reaction is

Answer: (B)

Solution

The reaction involves the conversion of a compound with multiple triple bonds to a compound with a single double bond using $\mathrm{NaNH_2}$ and $\mathrm{Na/liq.NH_3}$. (B) is answer.

Question 40

Chemistry · Alcohols, Phenols and Ethers · Single correct

Among the following, the conformation that corresponds to the most stable conformation of $\textit{meso}$–butane–2,3–diol is –

Answer: (b)

Solution

The structure shown is a meso butane-2,3-diol. It is the most stable conformation with hydrogen bonding.

Question 41

Chemistry · The Solid State · Single correct

For the given close packed structure of a salt made of cation X and anion Y shown below (ions of only one face are shown for clarity), the packing fraction is approximately (packing fraction = $\frac{Packing efficiency}{100}$)

  1. 0.74
  2. 0.63
  3. 0.52
  4. 0.48

Answer: (b)

Solution

Packing fraction (P.F.) is given by $$\frac{\frac{4}{3} \pi r_-^3 + \frac{4}{3} \pi r_+^3}{a^3}$$ where $$\frac{r_+}{r_-} = 0.414$$ (square planar void), and $a = 2r_-$. We get, $$P.F. = \frac{\frac{4}{3} \pi \left(r_-^3 + 3r_+^3\right)}{8r_-^3}$$ $$= \left[ \frac{\pi}{6} \left(1 + 3(0.414)^3\right) \right]$$ $$= 0.63$$

Question 42

Chemistry · Co-ordination Compounds · Single correct

The calculated spin only magnetic moments of $[Cr(NH_3)_6]^{3+}$ and $[CuF_6]^{3-}$ in BM, respectively, are (Atomic numbers of Cr and Cu are 24 and 29, respectively)

  1. 3.87 and 2.84
  2. 4.90 and 1.73
  3. 3.87 and 1.73
  4. 4.90 and 2.84

Answer: (a)

Solution

[$\mathrm{Cr(NH_3)_6}$]^{3+} $\rightarrow$ $\mathrm{Cr^{3+}}$ $\Rightarrow$ [$\mathrm{Ar}$]3d^3 In presence of NH_3 ligand $\square$ $\square$ e_g $\boxed{\uparrow \uparrow \uparrow}$ t_{2g} Number of unpaired electrons = 3 $\mu$ = $\sqrt{n(n+2)}$ B.M. $\mu$ = $\sqrt{3(3+2)}$ B.M. $\mu$ = $\sqrt{15}$ B.M. $\Rightarrow$ 3.87 B.M. [$\mathrm{CuF_6}$]^{3-} $\mathrm{Cu^{3+}}$ $\Rightarrow$ [$\mathrm{Ar}$]3d^8 In presence of $\mathrm{F^-}$ Ligand $\mathrm{Cu^{3+}}$ $\Rightarrow$ $\boxed{\uparrow \uparrow}$ e_g $\boxed{\downarrow \downarrow \downarrow \downarrow}$ t_{2g} Number of unpaired electrons = 2 $\mu$ = $\sqrt{n(n+2)}$ B.M. $\mu$ = $\sqrt{2(2+2)}$ $\Rightarrow$ $\sqrt{8}$ B.M. $\Rightarrow$ 2.84 B.M.

Question 43

Chemistry · Some Basic Concepts of Chemistry · Fill in the blank

For the following reaction scheme, percentage yields are given along the arrow: $x$ and $y$ are the mass of $\mathrm{R}$ and $\mathrm{U}$ respectively. Use: Molar mass (in $\mathrm{g\,mol^{-1}}$) of H, C and O as 1, 12 and 16, respectively. The value of x is _____.

Answer: 1.62, 1.62, 1.6, 1.62

Solution

The reaction is given by: $$\mathrm{Mg_2C_3 + 4H_2O \rightarrow 2Mg(OH)_2 + CH_3C \equiv CH}$$ The reaction of acetylene with sodium amide and methyl iodide is: $$\mathrm{CH_3C \equiv CH \xrightarrow{NaMe_2} CH_3 - C \equiv CNa^+ \xrightarrow{MeI} CH_3 - C \equiv C - CH_3 (0.075 mmol)}$$ This compound (Q) undergoes further reaction: $$\mathrm{3CH_3 - C \equiv C - CH_3 \xrightarrow{red hot iron tube, 873K}}$$ The product is: $$\mathrm{(0.075 \times 0.4) \times = 0.01 mole}$$ The value of $x$ is calculated as: $$x = 162 \times 0.01 = 1.62 gm$$

Question 44

Chemistry · Some Basic Concepts of Chemistry · Numerical

For the following reaction scheme, percentage yields are given along the arrow: $x$ and $y$ are the mass of $\mathrm{R}$ and $\mathrm{U}$ respectively. Use: Molar mass (in $\mathrm{g\,mol^{-1}}$) of H, C and O as 1, 12 and 16, respectively. The value of y is ______.

Answer: 3.2, 3.2, 3.2, 3.2, 3.2

Solution

Given (P) 0.1 mole. Using Kucherov reaction with $Hg^{2+}/H^+$ at 333K, 100%, we obtain $CH_3C=CH_3$ (0.01 mole). This undergoes a reaction with $Ba(OH)_2/\Delta$ to form $CH_3C=CH-CH_3$ (0.04 mole) and further reacts to form $CH_3C=CH-OH + CHCl_3$. Calculating the moles: $$0.1 \times \frac{82}{100} \times \frac{1}{2} = 0.04 mole$$ Further calculation: $$0.04 \times \frac{80}{100} = 0.032 mole$$ The sum $60 + 32 + 8 = 100$. The value of $Y = 0.032 \times 100 = 3.2$.

Question 45

Chemistry · Thermodynamics · Fill in the blank

For the reaction $\mathrm{X(s) \rightleftharpoons Y(s) + Z(g)}$, the plot of $\ln \frac{p_z}{p^\Theta}$ versus $\frac{10^4}{T}$ is given below (in solid line), where $p_z$ is the pressure (in bar) of the gas $\mathrm{Z}$ at temperature $T$ and $p^\Theta = 1$ bar. (Given, $\frac{\mathrm{d}(\ln K)}{\mathrm{d}\left(\frac{1}{T}\right)} = -\frac{\Delta H^\Theta}{R}$, where the equilibrium constant, $K = \frac{p_z}{p^\Theta}$ and the gas constant, $R = 8.314$ J K$^{-1}$ mol$^{-1}$) The value of standard enthalpy, $\Delta H^\Theta$ (in kJ mol$^{-1}$) for the reaction is _____.

Answer: 166.28

Solution

Given $\Delta G^\circ = -RT \ln \left( \frac{P}{1} \right) = \Delta H^\circ - T \Delta S^\circ$. $\newline$ $\ln$ $\left$( $\frac{P}{1}$ $\right$) = -$\frac{\Delta H^\circ}{RT}$ + $\frac{\Delta S^\circ}{R}$$. \newline Slope $= -$\frac{\Delta H^\circ}{R}$ = 10^4 $\times$ $\left$( $\frac{-4}{2}$ $\right$)$. \newline \Rightarrow \Delta H^\circ = 2 \times 10^4 \times R = 166.28 \, \mathrm{kJ/mole}$

Question 46

Chemistry · Thermodynamics · Numerical

For the reaction $\mathrm{X(s)} \rightleftharpoons \mathrm{Y(s)} + \mathrm{Z(g)}$, the plot of $\ln \frac{p_z}{p^\Theta}$ versus $\frac{10^4}{T}$ is given below (in solid line), where $p_z$ is the pressure (in bar) of the gas $\mathrm{Z}$ at temperature $T$ and $p^\Theta = 1 \, \mathrm{bar}$. (Given, $\frac{\mathrm{d}(\ln K)}{\mathrm{d}\left(\frac{1}{T}\right)} = -\frac{\Delta H^\Theta}{R}$, where the equilibrium constant, $K = \frac{p_z}{p^\Theta}$ and the gas constant, $R = 8.314 \, \mathrm{J} \, \mathrm{K}^{-1} \, \mathrm{mol}^{-1}$) The value of $\Delta S^\Theta$ (in $\mathrm{J} \, \mathrm{K}^{-1} \, \mathrm{mol}^{-1}$) for the given reaction, at $1000 \, \mathrm{K}$ is ______.

Answer: 141.33

Solution

From the plot when, $\frac{10^4}{T} = 10$ implies $T = 1000 \, \mathrm{K}$. $$\ln \left( \frac{P_2}{1} \right) = -3$$ Substituting in equation: $$\ln \left( \frac{P_2}{1} \right) = -\frac{\Delta H^o}{RT} + \frac{\Delta S^o}{R}$$ We get, $$-3 = -\frac{2 \times 10^4 \times R}{R \times 1000} + \frac{\Delta S^o}{R}$$ $$\Rightarrow \Delta S^o = 17R$$ $$\Rightarrow \Delta S^o = 17 \times 8.314 \, \mathrm{J/K\cdot mol}$$ $$\Rightarrow \Delta S^o = 141.34 \, \mathrm{J/K\cdot mol}$$

Question 47

Chemistry · Solutions · Numerical

The boiling point of water in a 0.1 molal silver nitrate solution (solution A) is $x \, ^\circ \mathrm{C}$. To this solution A, an equal volume of 0.1 molal aqueous barium chloride solution is added to make a new solution B. The difference in the boiling points of water in the two solutions A and B is $y \times 10^{-2} \, ^\circ \mathrm{C}$. (Assume : Densities of the solutions A and B are the same as that of water and the soluble salts dissociate completely.) Use: Molal elevation constant (Ebullioscopic Constant), $K_b = 0.5 \, \mathrm{K \, kg \, mol^{-1}}$; Boiling point of pure water as $100^\circ \mathrm{C}$.) The value of $x$ is _______.

Answer: 100.1

Solution

The dissociation of $\mathrm{AgNO_3(aq)}$ results in $\mathrm{Ag^+(aq)}$ and $\mathrm{NO_3^-(aq)}$ with concentrations of $0.1 \, \mathrm{m}$ each. The boiling point elevation $\Delta T_b$ is calculated as $0.2 \times 0.5 = 0.1^\circ \mathrm{C} = 0.1 \, \mathrm{K}$. Therefore, the boiling point of the solution is $100.1^\circ \mathrm{C}$, which is equal to $X$.

Question 48

Chemistry · Some Basic Concepts of Chemistry · Fill in the blank

The boiling point of water in a 0.1 molal silver nitrate solution (solution A) is $x \, ^\circ \mathrm{C}$. To this solution A, an equal volume of 0.1 molal aqueous barium chloride solution is added to make a new solution B. The difference in the boiling points of water in the two solutions A and B is $y \times 10^{-2} \, ^\circ \mathrm{C}$. (Assume: Densities of the solutions A and B are the same as that of water and the soluble salts dissociate completely.) Use: Molal elevation constant (Ebullioscopic Constant), $K_b = 0.5 \, \mathrm{K \, kg \, mol^{-1}}$; Boiling point of pure water as $100 \, ^\circ \mathrm{C}$. The value of $|y|$ is

Answer: 2.5

Solution

AgNO_3($\mathrm{aq}$) $\longrightarrow$ $\mathrm{Ag^+ (aq)}$ + $\mathrm{NO_3^- (aq)}$ 0.05 $\,$ $\mathrm{m}$ 0.05 $\,$ $\mathrm{m}$ 0.05 $\,$ $\mathrm{m}$ $\mathrm{BaCl_2(aq)}$ $\longrightarrow$ $\mathrm{Ba^{2+}(aq)}$ + 2$\mathrm{Cl^-(aq)}$ 0.05 $\,$ $\mathrm{m}$ 0.05 $\,$ $\mathrm{m}$ 0.1 $\,$ $\mathrm{m}$ $\mathrm{Ag^+}$ and $\mathrm{Cl^-}$ combine to form AgCl precipitate $\mathrm{Ag^+(aq)}$ + $\mathrm{Cl^-(aq)}$ $\longrightarrow$ $\mathrm{AgCl(s)}$ t = 0 0.05 $\,$ $\mathrm{m}$ 0.1 $\,$ $\mathrm{m}$ t = $\infty$ 0 0.05 $\,$ $\mathrm{m}$ In final solution total concentration of all ions: [$\mathrm{Cl^-}$] + [$\mathrm{NO_3^-}$] + [$\mathrm{Ba^{2+}}$] = 0.05 + 0.05 + 0.05 = 0.15 $\,$ $\mathrm{m}$ $\Delta$ T_b = 0.5 $\times$ 0.15 = 0.075 $\,$ ^$\circ$ $\mathrm{C}$ B.P. of solution 'B' = 100.075^$\circ$ $\mathrm{C}$ B.P. of solution 'A' = 100.1^$\circ$ $\mathrm{C}$ |y| = 100.1 - 100.075 = 0.025 = 2.5 $\times$ 10^{-2}

Question 49

Chemistry · Biomolecules · Multiple correct

Given The compound(s), which on reaction with HNO$_3$ will give the product having degree of rotation, $[\alpha]_D = -52.7^\circ$ is (are)

Answer: (c), (d)

Solution

The enantiomer of P has a rotation of $-52.7^\circ$ as follows. The compound with $[\alpha]_D = 52.7^\circ$ is shown. The reaction with dil. $\mathrm{HNO_3}$ leads to the formation of the enantiomer with the opposite rotation.

Question 50

Chemistry · Analytical Chemistry · Multiple correct

The reaction of Q with PhSNa yields an organic compound (major product) that gives positive Carius test on treatment with Na_2O_2 followed by addition of BaCl_2. The correct option(s) for Q is (are).

Answer: (a), (d)

Solution

Both options (A) and (D) give a positive Carius test.

Question 51

Chemistry · Surface Chemistry · Multiple correct

The correct statement(s) related to colloids is(are)

  1. The process of precipitating colloidal sol by an electrolyte is called peptization.
  2. Colloidal solution freezes at higher temperature than the true solution at the same concentration.
  3. Surfactants form micelle above critical micelle concentration (CMC). CMC depends on temperature
  4. Micelles are macromolecular colloids.

Answer: (b), (c)

Solution

(A) Process of precipitating colloidal solution is called coagulation. Hence false. (B) For colloidal solutions concentration is very small due to very large molar mass and hence their colligative properties are very small as compared to true solutions. Therefore, $\Delta T_f$ is lesser for colloidal solution. Hence true. (C) At CMC surfactant form micelles. Hence true. (D) Micelles and macromolecular colloids are two different types of colloids. Hence false.

Question 52

Chemistry · Thermodynamics · Multiple correct

An ideal gas undergoes a reversible isothermal expansion from state I to state II followed by a reversible adiabatic expansion from state II to state III. The correct plot(s) representing the changes from state I to state III is(are) (p : pressure, V : volume, T : temperature, H : enthalpy, S : entropy)

Answer: (a), (b), (d)

Solution

From state I to II (Reversible isothermal expansion) P decreases, V increases, T constant H constant & S increases. From state II to III (Reversible adiabatic expansion) P decreases, V increases, T decreases H decreases, S constant Therefore, plots (A), (B), (D) are correct while (C) is wrong as from II to III, H is decreasing.

Question 53

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

The correct statement(s) related to the metal extraction processes is(are)

  1. A mixture of PbS and PbO undergoes self-reduction to produce Pb and SO_2.
  2. In the extraction process of copper from copper pyrites, silica is added to produce copper silicate.
  3. Partial oxidation of sulphide ore of copper by roasting, followed by self-reduction produces blister copper.
  4. In cyanide process, zinc powder is utilized to precipitate gold from Na[Au(CN)_2]

Answer: (a), (c), (d)

Solution

(A) $\mathrm{PbS} + 2\mathrm{PbO} \rightarrow 3\mathrm{Pb} + \mathrm{SO_2}$ (self reduction) (B) Silica is added to remove impurity of Fe in the form of slag $\mathrm{FeSiO_3}$ (C) $\mathrm{CuFeS_2}$ ore is partially oxidized first by roasting and then self reduction of Cu takes place to produce blister copper. (D) $4 \mathrm{Na} [\mathrm{Au} (\mathrm{CN})_2] + 2 \mathrm{Zn} \rightarrow 2 \mathrm{Na}_2[\mathrm{Zn(CN)}_4] + 4 \mathrm{Au}$

Question 54

Chemistry · Analytical Chemistry · Multiple correct

A mixture of two salts is used to prepare a solution S, which gives the following results: White precipitate(s) only $\xleftarrow[Room temperature]{Dilute NaOH(aq.)}$ S (aq. solution of the salts) $\xrightarrow[Room temperature]{Dilute HCl(aq.)}$ White precipitate(s) only The correct option(s) for the salt mixture is(are)

  1. Pb(NO$_3$)$_2$ and Zn(NO$_3$)$_2$
  2. Pb(NO$_3$)$_2$ and Bi(NO$_3$)$_3$
  3. AgNO$_3$ and Bi(NO$_3$)$_3$
  4. Pb(NO$_3$)$_2$ and Hg(NO$_3$)$_2$

Answer: (a), (b)

Solution

Pb(NO_3)_2 $\xrightarrow{dil. HCl}$ PbCl_2 $\downarrow$ White Ppt. Bi(NO_3)_3 $\xrightarrow{dil. HCl}$ BiCl_3 Water Soluble Hg(NO_3)_2 $\xrightarrow{dil. HCl}$ HgCl_2 Water Soluble AgNO_3 $\xrightarrow{dil. HCl}$ AgCl $\downarrow$ White Ppt. Zn(NO_3)_2 $\xrightarrow{dil. HCl}$ ZnCl_2 Water Soluble Pb(NO_3)_2 $\xrightarrow{NaOH(dil.)}$ Pb(OH)_2 $\downarrow$ White Ppt. Zn(NO_3)_2 $\xrightarrow{NaOH(dil.)}$ Zn(OH)_2 $\downarrow$ White Ppt. Bi(NO_3)_3 $\xrightarrow{NaOH(dil.)}$ Bi(OH)_3 $\downarrow$ White Ppt. AgNO_3 $\xrightarrow{NaOH(dil.)}$ Ag_2O $\downarrow$ Brown Ppt. Hg(NO_3)_2 $\xrightarrow{NaOH(dil.)}$ HgO $\downarrow$ Yellow Ppt.

Question 55

Chemistry · Haloalkanes and Haloarenes · Numerical

The maximum number of possible isomers (including stereoisomers) which may be formed on mono-bromination of 1-methylcyclohex-1-ene using $\mathrm{Br}_2$ and UV light is

Solution

The reaction begins with the bromination of the methylcyclohexane using $\mathrm{Br_2}$ and $hv$. This results in the formation of several products. 1. The first product is formed by the substitution of a hydrogen atom with a bromine atom on the methyl group, resulting in $\mathrm{CH_2Br}$. 2. The second product involves the formation of a radical on the methyl group, which then reacts with $\mathrm{Br_2}$ to form $\mathrm{CH_2Br}$ with $R/S$ configuration. 3. Another product is formed by the substitution on the ring, resulting in a bromine atom attached to the ring with $R/S$ configuration. 4. Additional products are formed by further substitution reactions on the ring and the methyl group, each resulting in different stereochemical configurations. 5. The total number of distinct products formed is 13, considering all stereochemical variations.

Question 56

Chemistry · Chemical Bonding and Molecular Structure · Fill in the blank

In the reaction given below, the total number of atoms having $sp^2$ hybridization in the major product P is ___

Answer: 12, 12.0, 12 atoms

Solution

The reaction involves the conversion of the given compound using $\mathrm{O_3}$ (excess) followed by $\mathrm{Zn/H_2O}$ to form an intermediate. This intermediate is then reacted with $\mathrm{NH_2OH}$ to form the final product. Total 12 atoms are $sp^2$ hybridised.

Question 57

Chemistry · Co-ordination Compounds · Numerical

The total number of possible isomers for $[Pt(NH_3)_4Cl_2]Br_2$ is