JEE Main 24 January 2023 Shift 2 question paper with solutions

JEE Main 24 January 2023 Shift 2: all 90 questions in paper order (Physics, Chemistry, Maths) with the answer key and worked solutions. Free to read; attempt it as a timed 3-hour mock test.

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Physics

Question 1

Physics · Mathematics in Physics · Single correct

If two vectors $\vec{P} = \hat{i} + 2m\hat{j} + m\hat{k}$ and $\vec{Q} = 4\hat{i} - 2\hat{j} + m\hat{k}$ are perpendicular to each other. Then, the value of $m$ will be:

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

Answer: (d)

Solution

Given $\vec{P} \cdot \vec{Q} = 0$. $$\left( \hat{i} + 2m \hat{j} + m \hat{k} \right) \cdot \left( 4 \hat{i} - 2 \hat{j} + m \hat{k} \right) = 0$$ This implies: $$4 - 4m + m^2 = 0$$ Solving the equation: $$(m - 2)^2 = 0 \implies m = 2$$

Question 2

Physics · Physical World, Units and Measurements · Single correct

The frequency ($\nu$) of an oscillating liquid drop may depend upon radius ($r$) of the drop, density ($\rho$) of liquid and the surface tension ($s$) of the liquid as : $$\nu = r^a \rho^b s^c.$$ The values of $a$, $b$ and $c$ respectively are

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

Answer: (a)

Solution

Given $\($[T^{-1}] = [L^1]^a [M^1 L^{-3}]^b $\left$[ $\frac{MLT^{-2}}{L}$ $\right$]^c$\)$. This implies $\($T^{-1} = M^{b+c} $\cdot$ L^{a-3b} $\cdot$ T^{-2c}$\)$. Given $\($c = $\frac{1}{2}$, b = -$\frac{1}{2}$, a - 3b = 0$\)$. Then $\($a + $\frac{3}{2}$ = 0 $\Rightarrow$ a = -$\frac{3}{2}$$\)$.

Question 3

Physics · Motion in a Straight Line · Single correct

The velocity time graph of a body moving in a straight line is shown in figure. The ratio of displacement to distance travelled by the body in time 0 to 10s is

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

Answer: (d)

Solution

Displacement $= \Sigma area = 16 - 8 + 16 - 8 = 16 \, \mathrm{m}$ Distance $= \Sigma |area| = 48 \, \mathrm{m}$ $$\frac{displacement}{Distance} = \frac{1}{3}$$

Question 4

Physics · Laws of Motion · Single correct

A body of mass 200 g is tied to a spring of spring constant 12.5 \, $\mathrm{N/m}$, while the other end of spring is fixed at point O. If the body moves about O in a circular path on a smooth horizontal surface with constant angular speed 5 \, $\mathrm{rad/s}$, then the ratio of extension in the spring to its natural length will be:

  1. 1:2
  2. 1:1
  3. 2:3
  4. 2:5

Answer: (c)

Solution

Natural length = $L_0$ Extension = $x$ $$kx = m(L_0 + x)\omega^2$$ $$\Rightarrow 12.5x = \frac{1}{5}(L_0 + x)25 \Rightarrow 1.5x = L_0$$ $$\Rightarrow \frac{x}{L_0} = \frac{2}{3}$$

Question 5

Physics · Work, Energy and Power · Numerical

A body of mass 1 kg begins to move under the action of a time dependent force $\vec{F} = (t \hat{i} + 3t^2 \hat{j}) \, \mathrm{N}$. where $\hat{i}$ and $\hat{j}$ are the unit vectors along x and y axis. The power developed by above force, at the time $t = 2 \, \mathrm{s}$. will be $\,$ $\mathrm{W}$.

Answer: 100

Solution

Given $\mathbf{F} = t \hat{i} + 3t^2 \hat{j}$. The equation $m \frac{d\mathbf{v}}{dt} = t \hat{i} + 3t^2 \hat{j}$ is given. With $m = 1 kg$, we have: $$\int_0^{\mathbf{v}} dv = \int_0^t t dt \hat{i} + \int_0^t 3t^2 dt \hat{j}$$ This results in: $$\mathbf{v} = \frac{t^2}{2} \hat{i} + t^3 \hat{j}$$ The power is given by: $$Power = \mathbf{F} \cdot \mathbf{V} = \frac{t^3}{2} + 3t^5$$ At $t = 2$, the power is: $$\frac{8}{2} + 3 \times 32$$ This equals $100$.

Question 6

Physics · System of Particles and Rotational Motion · Numerical

A uniform solid cylinder with radius $R$ and length $L$ has moment of inertia $I_1$, about the axis of cylinder. A concentric solid cylinder of radius $R' = \frac{R}{2}$ and length $L' = \frac{L}{2}$ is caned out of the original cylinder. If $I_2$ is the moment of inertia of the carved out portion of the cylinder then $\frac{I_1}{I_2} =$ (Both $I_1$ and $I_2$ are about the axis of the cylinder)

Answer: 32

Solution

Given the two cylinders, the moment of inertia for the first cylinder is $$I_1 = \frac{m_1 R^2}{2}$$ and for the second cylinder is $$I_2 = \frac{m_2 \left(\frac{R}{2}\right)^2}{2}.$$ The ratio of the moments of inertia is $$\frac{I_1}{I_2} = \frac{4m_1}{m_2} = \frac{4 \cdot \rho \pi R^2 \ell}{\rho \cdot \frac{\pi R^2}{4} \times \frac{\ell}{2}} \Rightarrow \frac{I_1}{I_2} = 32.$$

Question 7

Physics · Gravitation · Single correct

Given below are two statements: Statement I: Acceleration due to earth's gravity decreases as you go 'up' or 'down' from earth's surface. Statement II: Acceleration due to earth's gravity is same at a height 'h' and depth 'd' from earth's surface, if h = d. In the light of above statements, choose the most appropriate answer form the options given below

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

Answer: (c)

Solution

Given the equations for gravitational acceleration: $$g' = \frac{g}{\left(1 + \frac{h}{R}\right)^2}$$ $$g' = g \left\{ 1 - \frac{d}{R} \right\}$$ The graph shows the variation of $g$ with respect to $r$ where $r = R$. Statement I is correct and Statement II is incorrect.

Question 8

Physics · Gravitation · Single correct

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: A pendulum clock when taken to Mount Everest becomes fast. Reason R: The value of $g$ (acceleration due to gravity) is less at Mount Everest than its value on the surface of earth. In the light of the above statements, choose the most appropriate answer from the options given below

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

Answer: (c)

Solution

The period $T$ is proportional to the inverse of the square root of $g$: $$T \propto \frac{1}{\sqrt{g}}.$$

Question 9

Physics · Gravitation · Single correct

If the distance of the earth from Sun is $1.5 \times 10^6$ km. Then the distance of an imaginary planet from Sun, if its period of revolution is 2.83 years is:

  1. $6 \times 10^7$ km
  2. $6 \times 10^6$ km
  3. $3 \times 10^6$ km
  4. $3 \times 10^7$ km

Answer: (c)

Solution

Given $T^2 \propto R^3$, we have: $$\left( \frac{T_1}{T_2} \right)^2 = \left( \frac{R_1}{R_2} \right)^3$$ Substituting the given values: $$\left( \frac{1}{2.83} \right)^2 = \frac{(1.5 \times 10^6)^3}{R_2}$$ Solving for $R_2$: $$R_2 = \left[ (2.83)^2 \times (1.5 \times 10^6)^3 \right]^{1/3}$$ Calculating the final value: $$= 8^{1/3} \times 1.5 \times 10^6 = 3 \times 10^6 \, km$$

Question 10

Physics · Mechanical Properties of Solids · Single correct

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: Steel is used in the construction of buildings and bridges. Reason R: Steel is more elastic and its elastic limit is high. In the light of above statements, choose the most appropriate answer from the options given below

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

Answer: (c)

Solution

Concept based

Question 11

Physics · Mechanical Properties of Fluids · Numerical

A Spherical ball of radius 1 mm and density 10.5 g/cc is dropped in glycerine of coefficient of viscosity 9.8 poise and density 1.5 g/cc. Viscous force on the ball when it attains constant velocity is 3696 x 10^{-x} N. The value of x is (Given, g = 9.8 m/s^2 and $\pi$ = $\frac{22}{7}$)

Answer: 7

Solution

When the ball attains terminal velocity $$F_v = (mg - F_B) (\because a = 0)$$ $$= V \sigma_b g - V \rho_\ell g$$ $$= Vg (\sigma_b - \rho_\ell)$$ $$= \frac{4}{3} \pi (10^{-3})^3 \times 9.8 \times (10.5 - 1.5) \times 10^3$$ $$= 3696 \times 10^{-7} \, \mathrm{N}$$ So, $x = 7$

Question 12

Physics · Thermodynamics · Single correct

In an Isothermal change, the change in pressure and volume of a gas can be represented for three different temperature; $T_3 > T_2 > T_1$ as:

Answer: (d)

Solution

Question 13

Physics · Thermodynamics · Single correct

Let $\gamma_1$ be the ratio of molar specific heat at constant pressure and molar specific heat at constant volume of a monoatomic gas and $\gamma_2$ be the similar ratio of diatomic gas. Considering the diatomic gas molecule as a rigid rotator, the ratio, $\frac{\gamma_1}{\gamma_2}$ is

  1. $\frac{27}{35}$
  2. $\frac{35}{27}$
  3. $\frac{25}{21}$
  4. $\frac{21}{25}$

Answer: (c)

Solution

For monoatomic gas $\gamma_1 = \frac{5}{3}$. For diatomic gas at low temperatures $\gamma_2 = \frac{7}{5}$. Therefore, $$\frac{\gamma_1}{\gamma_2} = \frac{\frac{5}{3}}{\frac{7}{5}} = \frac{25}{21}.$$

Question 14

Physics · Oscillations · Fill in the blank

A mass m attached to free end of a spring executes SHM with a period of 1s. If the mass is increased by 3 kg the period of oscillation increases by one second, the value of mass m is _______ kg.

Answer: 1

Solution

Given $T = 2\pi \sqrt{\frac{m}{k}} = 1$ and $T' = 2\pi \sqrt{\frac{m+3}{k}} = 2$. The ratio $\frac{T}{T'} = \sqrt{\frac{m}{m+3}} = \frac{1}{2}$. This implies $\frac{m}{m+3} = \frac{1}{4}$. Solving for $m$, we get $m = 1$.

Question 15

Physics · Electric Charges and Fields · Single correct

The electric potential at the centre of two concentric half rings of radii $R_1$ and $R_2$, having same linear charge density $\lambda$ is

  1. $\frac{2\lambda}{\varepsilon_0}$
  2. $\frac{\lambda}{2\varepsilon_0}$
  3. $\frac{\lambda}{4\varepsilon_0}$
  4. $\frac{\lambda}{\varepsilon_0}$

Answer: (b)

Solution

Potential at centre $$V = \frac{(\lambda \cdot \pi R_2)}{4 \pi \varepsilon_0 R_2} + \frac{(\lambda \cdot \pi R_1)}{4 \pi \varepsilon_0 R_1}$$ $$= \frac{\lambda}{2 \varepsilon_0}$$

Question 16

Physics · Electrostatic Potential and Capacitance · Numerical

A parallel plate capacitor with air between the plate has a capacitance of 15 $\mathrm{pF}$. The separation between the plate becomes twice and the space between them is filled with a medium of dielectric constant $3.5$. Then the capacitance becomes $\frac{x}{4}$$\mathrm{pF}$. The value of $x$ is.

Answer: 105

Solution

Given $C_0 = \frac{\varepsilon_0 A}{d} = 15 \, \mathrm{pF}$. Then, $C = \frac{K \varepsilon_0 A}{2d} = \frac{3.5}{2} \times 15 \, \mathrm{pF} = \frac{105}{4} \, \mathrm{pF}$.

Question 17

Physics · Current Electricity · Single correct

A cell of emf 90 V is connected across series combination of two resistors each of 100 $\Omega$ resistance. A voltmeter of resistance 400 $\Omega$ is used to measure the potential difference across each resistor. The reading of the voltmeter will be :

  1. 40 V
  2. 45 V
  3. 80 V
  4. 90 V

Answer: (a)

Solution

The equivalent resistance is calculated as follows: $$R_{eq} = \frac{400 \times 100}{500} + 100$$ $$= 180 \, \Omega$$ The current $i$ is given by: $$i = \frac{90}{180} = \frac{1}{2} \, A$$ The reading is calculated as: $$Reading = \frac{1}{2} \times \frac{400}{500} \times 100$$ $$= 40 \, volt$$

Question 18

Physics · Current Electricity · Numerical

If a copper wire is stretched to increase its length by 20$\%$. The percentage increase in resistance of the wire is $\%$.

Answer: 44

Solution

As volume is constant, so resistance is proportional to (length)$^2$. $$\Rightarrow % change in resistance = 20 + 20 + \frac{400}{100} = 44\%$$

Question 19

Physics · Moving Charges and Magnetism · Single correct

A long solenoid is formed by winding 70 turns cm$^{-1}$. If 2.0 A current flows, then the magnetic field produced inside the solenoid is ____________ ($\mu_0 = 4\pi \times 10^{-7} \, \mathrm{TmA}^{-1}$)

  1. 1232 $\times$ 10^{-4} $\,$ $\mathrm{T}$
  2. 176 $\times$ 10^{-4} $\,$ $\mathrm{T}$
  3. 352 $\times$ 10^{-4} $\,$ $\mathrm{T}$
  4. 88 $\times$ 10^{-4} $\,$ $\mathrm{T}$

Answer: (b)

Solution

Given $B = \mu_0 n I$. $$= 4 \pi \times 10^{-7} \times 70 \times 10^2 \times 2$$ $$= 56 \pi \times 10^{-4} \, \mathrm{T}$$ $$= 176 \times 10^{-4} \, \mathrm{T}$$

Question 20

Physics · Moving Charges and Magnetism · Numerical

A single turn current loop in the shape of a right angle triangle with sides 5 cm, 12 cm, 13 cm is carrying a current of 2 A. The loop is in a uniform magnetic field of magnitude 0.75 T whose direction is parallel to the current in the 13 cm side of the loop. The magnitude of the magnetic force on the 5 cm side will be $\frac{x}{130}$ N. The value of x is

Answer: 9

Solution

Force on 5 cm side is $|\vec{F}| = ILB \sin \theta$. $$= (2)(5 \times 10^{-2}) \times \frac{3}{4} \times \frac{12}{13} = \frac{9}{130} \, \mathrm{N}$$ So, $x = 9$

Question 21

Physics · Electromagnetic Induction · Single correct

A metallic rod of length 'L' is rotated with an angular speed of ‘$\omega$’ normal to a uniform magnetic field 'B' about an axis passing through one end of rod as shown in figure. The induced emf will be :

  1. $\frac{1}{4} B^2 L \omega$
  2. $\frac{1}{4} B L^2 \omega$
  3. $\frac{1}{2} B L^2 \omega$
  4. $\frac{1}{2} B^2 L^2 \omega$

Answer: (c)

Solution

The integral of the electromotive force is given by $$\int d\varepsilon = \int B(\omega x) \, dx$$. Evaluating the integral, we have $$\varepsilon = B \omega \int_0^L x \, dx = \frac{B \omega L^2}{2}.$$

Question 22

Physics · Alternating Current · Numerical

Three identical resistors with resistance $R = 12 \, \Omega$ and two identical inductors with self inductance $L = 5 \, \mathrm{mH}$ are connected to an ideal battery with emf of $12 \, \mathrm{V}$ as shown in figure. The current through the battery long after the switch has been closed will be ________ A.

Answer: 3

Solution

After long time an inductor behaves as a resistance-less path. So current through cell $$I = \frac{12}{R/3} = 3 \, \mathrm{A} \{\because R = 12 \, \Omega\}$$

Question 23

Physics · Electromagnetic Waves · Single correct

The electric field and magnetic field components of an electromagnetic wave going through vacuum is described by $$E_x = E_0 \sin (kz - \omega t)$$ $$B_y = B_0 \sin (kz - \omega t)$$ Then the correct relation between $E_0$ and $B_0$ is given by

  1. $kE_0 = \omega B_0$
  2. $E_0 B_0 = \omega k$
  3. $\omega E_0 = kB_0$
  4. $E_0 = kB_0$

Answer: (a)

Solution

Given the equation for C: $$C = \frac{\omega}{k} = \frac{E_0}{B_0}$$

Question 24

Physics · Ray Optics and Optical Instruments · Single correct

When a beam of white light is allowed to pass through convex lens parallel to principal axis, the different colours of light converge at different point on the principle axis after refraction. This is called:

  1. Scattering
  2. Chromatic aberration
  3. Spherical aberration
  4. Polarisation

Answer: (b)

Solution

Based on fact.

Question 25

Physics · Ray Optics and Optical Instruments · Numerical

A convex lens of refractive index 1.5 and focal length 18 cm in air is immersed in water. The change in focal length of the lens will be _____ cm. (Given refractive index of water = $\frac{4}{3}$)

Answer: 54

Solution

Given $\($ $\frac{1}{f_{\mathrm{H_2O}}}$ = $\left$( $\frac{\mu_g}{\mu_{\mathrm{H_2O}}}$ - 1 $\right$) $\left$( $\frac{2}{R}$ $\right$) $\)$ $\($ = $\frac{1}{8}$ $\left$( $\frac{2}{R}$ $\right$) $\)$ $\($ = $\frac{1}{(4f_{\mathrm{air}})}$ $\)$ So, $\($ f_{$\mathrm{H_2O}$} = 4f_{$\mathrm{air}$} = 72 \, $\mathrm{cm}$ $\)$ So change in focal length $\($ = 72 - 18 = 54 \, $\mathrm{cm}$ $\)$

Question 26

Physics · Dual Nature of Radiation and Matter · Single correct

An $\alpha$-particle, a proton and an electron have the same kinetic energy. Which one of the following is correct in case of their De-Broglie wavelength:

  1. $\lambda_{\alpha} > \lambda_{p} > \lambda_{e}$
  2. $\lambda_{\alpha} < \lambda_{p} < \lambda_{e}$
  3. $\lambda_{\alpha} = \lambda_{p} = \lambda_{e}$
  4. $\lambda_{\alpha} > \lambda_{p} < \lambda_{e}$

Answer: (b)

Solution

Given $\lambda_D = \frac{h}{p} = \frac{h}{\sqrt{2mK}}$. Therefore, $\lambda \propto \frac{1}{\sqrt{m}}$. Since $m_\alpha > m_p > m_e$, it follows that $\lambda_e > \lambda_p > \lambda_\alpha$.

Question 27

Physics · Atoms · Single correct

A photon is emitted in transition from $n = 4$ to $n=1$ level in hydrogen atom. The corresponding wavelength for this transition is (given, $h = 4 \times 10^{-15} \, \mathrm{eVs}$):

  1. 94.1 nm
  2. 941 nm
  3. 97.4 nm
  4. 99.3 nm

Answer: (a)

Solution

Given $( \frac{hc}{\lambda} = \left[ 1 - \frac{1}{16} \right] (13.6\ \mathrm{eV}) )$. So, $( \lambda = 94.1\ \mathrm{nm} )$.

Question 28

Physics · Nuclei · Numerical

The energy released per fission of nucleus of $^{240}\mathrm{X}$ is $200 \, \mathrm{MeV}$. The energy released if all the atoms in $120 \, \mathrm{g}$ of pure $^{240}\mathrm{X}$ undergo fission is _____ $\times \, 10^{25} \, \mathrm{MeV}$. (Given $N_A = 6 \times 10^{23}$)

Answer: 6

Solution

Number of moles is given by $$\frac{120}{240} = \frac{1}{2}$$. The number of molecules is $$\frac{1}{2} \times N_A$$. The energy released is $$\frac{1}{2} \times 6 \times 10^{23} \times 200$$ which equals $$6 \times 10^{25} \, MeV$$.

Question 29

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

The logic gate equivalent to the given circuit diagram is:

  1. OR
  2. NAND
  3. NOR
  4. AND

Answer: (b)

Solution

The truth table shows the values for $A_1$, $B_1$, and $Y$. The expression for $Y$ is given by: $$Y = \overline{A_1 \odot B_1} NAND$$

Question 30

Physics · Communication Systems · Single correct

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

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

Answer: (a)

Solution

AM Broadcast $540 - 1600 \, \mathrm{KHz}$ FM Broadcast $\rightarrow 88 - 108 \, \mathrm{MHz}$ Television $\rightarrow 54 - 890 \, \mathrm{MHz}$ Satellite communication $\rightarrow 3.7 - 4.2 \, \mathrm{GHz}$ Therefore: A-II, B-I, C-IV, D-III

Chemistry

Question 31

Chemistry · States of Matter · Numerical

Following figure shows spectrum of an ideal black body at four different temperatures. The number of correct statement/s from the following is _______.

  1. $T_4 > T_3 > T_2 > T_1$
  2. The black body consists of particles performing simple harmonic motion.
  3. The peak of the spectrum shifts to shorter wavelength as temperature increases.
  4. $\frac{T_1}{\nu_1} = \frac{T_2}{\nu_2} = \frac{T_3}{\nu_3} \neq constant$
  5. The given spectrum could be explained using quantisation of energy.

Answer: (b)

Solution

The spectrum of Black body radiation is explained using quantization of energy. With increase in temperature, peak of spectrum shifts to shorter wavelength or higher frequency. For above graph $\rightarrow T_1 > T_2 > T_3 > T_4$.

Question 32

Chemistry · Chemical Bonding and Molecular Structure · Single correct

What is the number of unpaired electron(s) in the highest occupied molecular orbital of the following species : $\mathrm{N_2}$ ; $\mathrm{N_2^+}$ ; $\mathrm{O_2}$ ; $\mathrm{O_2^+}$ ?

  1. 0, 1, 2, 1
  2. 2, 1, 2, 1
  3. 0, 1, 0, 1
  4. 2, 1, 0, 1

Answer: (a)

Solution

For $\mathrm{N_2}$: $$\sigma 1s^2 \, \sigma^* 1s^2 \, \sigma 2s^2 \, \sigma^* 2s^2 \, \pi 2p_x^2 = \pi 2p_y^2$$ $$\frac{\sigma 2p_z^2}{HOMO}$$ For $\mathrm{N_2^+}$: $$\sigma 1s^2 \, \sigma^* 1s^2 \, \sigma 2s^2 \, \sigma^* 2s^2 \, \pi 2p_x^2 = \pi 2p_y^2$$ $$\frac{\sigma 2p_z^1}{HOMO}$$ For $\mathrm{O_2}$: $$\sigma 1s^2 \, \sigma^* 1s^2 \, \sigma 2s^2 \, \sigma^* 2s^2 \, \sigma 2p_z^2$$ $$\pi 2p_x^2 = \pi 2p_y^2$$ $$\pi^* 2p_x^1 = \pi^* 2p_y^1 (HOMO)$$ For $\mathrm{O_2^+}$: $$\sigma 1s^2 \, \sigma^* 1s^2 \, \sigma 2s^2 \, \sigma^* 2s^2 \, \sigma 2p_z \, \pi 2p_x = \pi 2p_y^2$$ $$\pi^* 2p_x^1 = \pi^* 2p_y^0 (HOMO)$$ $\mathrm{N_2} \Rightarrow 0$ unpaired $e^-$ in HOMO $\mathrm{N_2^+} \Rightarrow 1$ unpaired $e^-$ in HOMO $\mathrm{O_2} \Rightarrow 2$ unpaired $e^-$ in HOMO $\mathrm{O_2^+} \Rightarrow 1$ unpaired $e^-$ in HOMO

Question 33

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

Sum of $\pi$-bonds present in peroxodisulphuric acid and pyrosulphuric acid is

Answer: 8

Solution

Question 34

Chemistry · States of Matter · Numerical

The number of statement's, which are correct with respect to the compression of carbon dioxide from point (a) in the Andrews isotherm from the following is ________.

  1. Carbon dioxide remains as a gas upto point (b)
  2. Liquid carbon dioxide appears at point (c)
  3. Liquid and gaseous carbon dioxide coexist between points (b) and (c)
  4. As the volume decreases from (b) to (c), the amount of liquid decreases

Answer: (b)

Solution

At $(a) \rightarrow \mathrm{CO_2}$ exists as gas. $(b) \rightarrow$ liquefaction of $\mathrm{CO_2}$ starts. $(c) \rightarrow$ liquefaction ends. $(d) \rightarrow \mathrm{CO_2}$ exists as liquid. Between $(b)$ and $(c) \rightarrow$ liquid and gaseous $\mathrm{CO_2}$ co-exist. As volume changes from $(b)$ to $(c)$, gas decreases and liquid increases. $(A), (C) \rightarrow$ correct.

Question 35

Chemistry · Thermodynamics · Numerical

One mole of an ideal monoatomic gas is subjected to changes as shown in the graph. The magnitude of the work done (by the system or on the system) is ______ J (nearest integer). Given: $\log 2 = 0.3$, $\ln 10 = 2.3$

Answer: 620

Solution

$1 \rightarrow 2 \Rightarrow$ Isobaric process $2 \rightarrow 3 \Rightarrow$ Isochoric process $3 \rightarrow 1 \Rightarrow$ Isothermal process $W = W_{1\to2} + W_{2\to3} + W_{3\to1}$ $= \left[-P(V_2-V_1)+0+\left(-P_1V_1\ln\left(\frac{V_2}{V_1}\right)\right)\right]$ $= \left[-1\times(40-20)+0+\left(-1\times20\ln\left(\frac{20}{40}\right)\right)\right]$ $= -20 + 20\ln2$ $= -20 + 20\times2.3\times0.3$ $= -6.2\ \text{bar L}$ $|W| = 6.2\ \text{bar L} = 620\ \text{J}$

Question 36

Chemistry · Equilibrium · Numerical

If the pKa of lactic acid is $5$, then the pH of $0.005\ \mathrm{M}$ calcium lactate solution at $25^\circ\mathrm{C}$ is ______ $\times10^{-1}$ (Nearest integer).

Answer: 85

Solution

Concentration of calcium lactate $=0.005\ \mathrm{M}$. Concentration of lactate ion $=(2\times0.005)\ \mathrm{M}$. Calcium lactate is a salt of weak acid + strong base. $\therefore$ Salt hydrolysis will take place. $\mathrm{pH}=7+\frac{1}{2}\left(\mathrm{p}K_a+\log C\right)$ $=7+\frac{1}{2}\left(5+\log(2\times0.005)\right)$ $=7+\frac{1}{2}\left(5-2\log10\right)$ $=7+\frac{1}{2}\times3$ $=8.5=85\times10^{-1}$

Question 37

Chemistry · Electrochemistry · Single correct

Choose the correct representation of conductometric titration of benzoic acid vs sodium hydroxide.

Answer: (b)

Solution

The reaction is given by $\mathrm{C_6H_5COOH} + \mathrm{NaOH} \rightarrow \mathrm{C_6H_5COONa} + \mathrm{H_2O}$. (A) $\rightarrow$ (B) Free $\mathrm{H^+}$ ions are replaced by $\mathrm{Na^+}$ which decreases conductance. (B) $\rightarrow$ $(C)$ Un-dissociated benzoic acid reacts with $\mathrm{NaOH}$ and forms salt which increases ions and conductance increases. $(C)$ $\rightarrow$ (D) After equivalence point at (3), $\mathrm{NaOH}$ added further increases $\mathrm{Na^+}$ and $\mathrm{OH^-}$ ions which further increases the conductance.

Question 38

Chemistry · Hydrogen · Single correct

In which of the following reactions the hydrogen peroxide acts as a reducing agent?

  1. $\mathrm{PbS} + 4\mathrm{H}_2\mathrm{O}_2 \rightarrow \mathrm{PbSO}_4 + 4\mathrm{H}_2\mathrm{O}$
  2. $2\mathrm{Fe}^{2+} + \mathrm{H}_2\mathrm{O}_2 \rightarrow 2\mathrm{Fe}^{3+} + 2\mathrm{OH}^-$
  3. $\mathrm{HOCl} + \mathrm{H}_2\mathrm{O}_2 \rightarrow \mathrm{H}_3\mathrm{O}^+ + \mathrm{Cl}^- + \mathrm{O}_2$
  4. $\mathrm{Mn}^{2+} + \mathrm{H}_2\mathrm{O}_2 \rightarrow \mathrm{Mn}^{4+} + 2\mathrm{OH}^-$

Answer: (c)

Solution

The reaction is given by: $$\mathrm{HOCl} + \mathrm{H_2O_2} \rightarrow \mathrm{H_3O^+} + \mathrm{Cl^-} + \mathrm{O_2}$$ In this reaction, $\mathrm{HOCl}$ acts as the oxidizing agent (O.A) and $\mathrm{H_2O_2}$ acts as the reducing agent (R.A). The $\mathrm{Cl}$ is reduced and the $\mathrm{O}$ is oxidized.

Question 39

Chemistry · The s-Block Elements · Multiple correct

Identify the correct statements about alkali metals. A. The order of standard reduction potential $(\mathrm{M^+ | M})$ for alkali metal ions is $\mathrm{Na > Rb > Li}$. B. $\mathrm{CsI}$ is highly soluble in water. C. Lithium carbonate is highly stable to heat. D. Potassium dissolved in concentrated liquid ammonia is blue in colour and paramagnetic. E. All the alkali metal hydrides are ionic solids. Choose the correct answer from the options given below

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

Answer: (c)

Solution

(1) $\mathrm{Na} > \mathrm{Cs} > \mathrm{Li}$ – true (If considered with sign) The low solubility of $\mathrm{CsI}$ is due to smaller hydration enthalpy of its two ions. $\mathrm{Li_2CO_3}$ is highly stable to heat – false In Conc. $\mathrm{NH_3}$, $\mathrm{K}$ formed blue solution – true

Question 40

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

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Beryllium has less negative value of reduction potential compared to the other alkaline earth metals. Reason R : Beryllium has large hydration energy due to small size of $\mathrm{Be}^{2+}$ but relatively large value of atomization enthalpy. In the light of the above statements, choose the most appropriate answer from the options given below.

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

Answer: (b)

Solution

Be has less negative value compared to other AEM. However, its reducing nature is due to large hydration energy associated with the small size of $\mathrm{Be^{2+}}$ ion and relatively large value of the atomization enthalpy of metal.

Question 41

Chemistry · Structure of Atom · Single correct

The number of s-electrons present in an ion with 55 protons in its unipositive state is

  1. 8
  2. 9
  3. 12
  4. 10

Answer: (d)

Solution

Given $Z = 55$ for $[\mathrm{Cs}]$, the configuration is $[\mathrm{Xe}] \, 6s^1$. For $[\mathrm{Cs}^+]$, the configuration is $[\mathrm{Xe}]$, i.e., up to $5s$ count $e^-$ of the $s$-subshell. This means $1s, 2s, 3s, 4s, 5s$ contribute to 10 electrons.

Question 42

Chemistry · Redox Reactions · Single correct

Which will undergo deprotonation most readily in basic medium?

  1. a only
  2. c only
  3. Both a and c
  4. b only

Answer: (a)

Solution

Most easily deprotonation. (More resonance stabilised)

Question 43

Chemistry · Hydrocarbons · Single correct

Given below are two statements: In the light of the above statements, choose the correct answer from the options given below:

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

Answer: (c)

Solution

For S-I, the reaction with $\mathrm{Zn-Hg}$ and conc. $\mathrm{HCl}$ does not lead to the reduction with hydrolysis of amide at high temperature only. Therefore, it is false. For S-II, the reaction with $\mathrm{NH_2NH_2}$ and $\mathrm{OH^-}$/Glycol does not lead to reduction with elimination. Therefore, it is false.

Question 44

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

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Benzene is more stable than hypothetical cyclohexatriene. Reason R : The delocalized $\pi$ electron cloud is attracted more strongly by nuclei of carbon atoms. In the light of the above statements, choose the correct answer from the options given below:

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

Answer: (c)

Solution

Assertion – A: Benzene is more stable than cyclohexatriene (True) Reason – R: Delocalised $\pi$–e cloud lies B.M.O so more attracted by nuclei of carbon atom. (True & Correct Explanation)

Question 45

Chemistry · Solutions · Numerical

The Total pressure observed by mixing two liquid A and B is $350 \, \mathrm{mm \, Hg}$ when their mole fractions are $0.7$ and $0.3$ respectively. The Total pressure becomes $410 \, \mathrm{mm \, Hg}$ if the mole fractions are changed to $0.2$ and $0.8$ respectively for A and B. The vapour pressure of pure A is _______ $\mathrm{mm \, Hg}$. (Nearest integer) Consider the liquids and solutions behave ideally.

Answer: 314

Solution

Let V.P. of pure A be $P_A^0$. Let V.P of pure B be $P_B^0$. When $X_A = 0.7$ and $X_B = 0.3$, $P_s = 350$. $$\Rightarrow P_A^0 \times 0.7 + P_B^0 \times 0.3 = 350 (i)$$ When $X_A = 0.2$ and $X_B = 0.8$, $P_s = 410$. $$\Rightarrow P_A^0 \times 0.2 + P_B^0 \times 0.8 = 410 (ii)$$ Solving (i) and (ii), $P_A^0 = 314 \, \mathrm{mm \, Hg}$, $P_B^0 = 434 \, \mathrm{mm \, Hg}$.

Question 46

Chemistry · Some Basic Concepts of Chemistry · Numerical

The number of units, which are used to express concentration of solutions from the following is __________. Mass percent, Mole, Mole fraction, Molarity, ppm, Molality.

Answer: 5

Solution

Mass percent, mole fraction, molarity, ppm, molality are used for measuring concentration terms.

Question 47

Chemistry · Chemical Kinetics and Nuclear Chemistry · Single correct

A student has studied the decomposition of a gas $AB_3$ at $25^\circ\mathrm{C}$. He obtained the following data. The order of the reaction is

  1. 0.5
  2. 2
  3. 1
  4. 0 (zero)

Answer: (b)

Solution

Given $t_{1/2} \propto (P_0)^{1-n}$. $$\frac{\left(t_{1/2}\right)_1}{\left(t_{1/2}\right)_2} = \frac{\left(P_0\right)_1^{1-n}}{\left(P_0\right)_2^{1-n}}$$ $$\Rightarrow \left(\frac{4}{2}\right) = \left(\frac{50}{100}\right)^{1-n}$$ $$\Rightarrow 2 = \left(\frac{1}{2}\right)^{1-n}$$ $$\Rightarrow 2 = (2)^{n-1}$$ $$\Rightarrow n-1 = 1$$ $$\Rightarrow n = 2$$

Question 48

Chemistry · Surface Chemistry · Numerical

The number of statement/s which are the characteristics of physisorption is __________.

  1. It is highly specific in nature
  2. Enthalpy of adsorption is high
  3. It decreases with increase in temperature
  4. It results into unimolecular layer
  5. No activation energy is needed

Answer: (b)

Solution

For physisorptions (a) Decreases with increase in temperature (b) No appreciable activation energy is required

Question 49

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

The metal which is extracted by oxidation and subsequent reduction from its ore is:

  1. Al
  2. Ag
  3. Cu
  4. Fe

Answer: (b)

Solution

Ag. $$4\mathrm{Ag} + 8\mathrm{CN}^- + \mathrm{O}_2 + 2\mathrm{H}_2\mathrm{O} \rightarrow 4[\mathrm{Ag(CN)}_2]^- + 4\mathrm{OH}^-$$ $$2[\mathrm{Ag(CN)}_2]^- + \mathrm{Zn} \rightarrow 2\mathrm{Ag} \downarrow + [\mathrm{Zn(CN)}_4]^{2-}$$

Question 50

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

Which one amongst the following are good oxidizing agents? A. $\mathrm{Sm}^{2+}$ B. $\mathrm{Ce}^{2+}$ C. $\mathrm{Ce}^{4+}$ D. $\mathrm{Tb}^{4+}$ Choose the most appropriate answer from the options given below:

  1. C only
  2. D only
  3. A and B only
  4. C and D only

Answer: (d)

Solution

$\mathrm{Ce^{+4}}$ and $\mathrm{Tb^{+4}}$ act as oxidising agent

Question 51

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

$K_2Cr_2O_7$ paper acidified with dilute $H_2SO_4$ turns green when exposed to

  1. Carbon dioxide
  2. Sulphur trioxide
  3. Hydrogen sulphide
  4. Sulphur dioxide

Answer: (d)

Solution

The reaction is given by: $$3\mathrm{SO_2} + \mathrm{Cr_2O_7^{2-}} + 2\mathrm{H^+} \rightarrow 3\mathrm{SO_4^{2-}} + 2\mathrm{Cr^{3+}} + \mathrm{H_2O}$$ The color of the solution is green.

Question 52

Chemistry · Co-ordination Compounds · Single correct

Which of the following cannot be explained by crystal field theory?

  1. The order of spectrochemical series
  2. Magnetic properties of transition metal complexes
  3. Colour of metal complexes
  4. Stability of metal complexes

Answer: (d)

Solution

Crystal field theory introduces the spectrochemical series based upon the experimental values of $\Delta$ but can't explain its order. While other three points are explained by CFT. Especially when the CFSE increases, thermodynamic stability of the complex increases.

Question 53

Chemistry · Co-ordination Compounds · Single correct

The hybridization and magnetic behaviour of cobalt ion in $[Co(NH_3)_6]^{3+}$ complex, respectively is

  1. $sp^3d^2$ and diamagnetic
  2. $d^2sp^3$ and paramagnetic
  3. $d^2sp^3$ and diamagnetic
  4. $sp^3d^2$ and paramagnetic

Answer: (c)

Solution

The complex $[\mathrm{Co(NH_3)_6}]^{3+}$ has a $d^2sp^3$ hybridization and is diamagnetic.

Question 54

Chemistry · Haloalkanes and Haloarenes · Numerical

Maximum number of isomeric monochloro derivatives which can be obtained from 2,2,5,5-tetramethylhexane by chlorination is

Answer: 3

Solution

The reaction of the given compound with $\mathrm{Cl_2/hv}$ leads to the formation of isomers. The first isomer is formed by the substitution of a chlorine atom at the terminal carbon, resulting in: $$\begin{array}{c} \mathrm{CH_3} \\ \mathrm{|} \\ \mathrm{CH_2 - C - CH_2 - CH_2 - C - CH_3} \\ \mathrm{|} \\ \mathrm{Cl} \\ \mathrm{CH_3} \end{array}$$ The second isomer is formed by the substitution of a chlorine atom at the chiral center, resulting in: $$\begin{array}{c} \mathrm{CH_3} \\ \mathrm{|} \\ \mathrm{CH_3 - C^* - CH - CH_2 - C - CH_3} \\ \mathrm{|} \\ \mathrm{CH_3} \\ \mathrm{Cl} \end{array}$$ This isomer is optically active, indicated by $(\pm)$. The total number of isomers is 3.

Question 55

Chemistry · Hydrocarbons · Single correct

Find out the major products from the following reactions.

Answer: (a)

Solution

The reaction involves the addition of water to an alkene. Using $BH_3, THF$ followed by $H_2O_2, HO^-$ results in an anti-Markovnikov product, which is compound (A). Using $Hg(OAc)_2, H_2O$ followed by $NaBH_4$ results in a Markovnikov product, which is compound (B).

Question 56

Chemistry · Amines · Single correct

Given below are two statements : Statement I : Pure Aniline and other arylamines are usually colourless. Statement II : Arylamines get coloured on storage due to atmospheric reduction. In the light of the above statements, choose the most appropriate answer from the options given below :

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

Answer: (c)

Solution

Statement 1 is (True) Pure aniline is colourless liquid. Statement 2 is (False) Aniline becomes dark brown due to action of air and light (oxidation).

Question 57

Chemistry · Amines · Single correct

Choose the correct colour of the product for the following reaction.

  1. Yellow
  2. White
  3. Red
  4. Blue

Answer: (c)

Solution

The reaction involves the coupling of a naphthylamine derivative with a diazonium salt. The diazonium salt is represented as $\mathrm{N=N-O-C-CH_3}$ with a sulfonic acid group $\mathrm{SO_3H}$. The reaction produces an azo compound with a red color, indicated by the presence of $\mathrm{SO_3H (Red)}$, and acetic acid $\mathrm{CH_3COOH}$ as a byproduct.

Question 58

Chemistry · Environmental Chemistry · Single correct

Correct statement is :

  1. An average human being consumes more food than air
  2. An average human being consumes nearly 15 times more air than food
  3. An average human being consumes equal amount of food and air
  4. An average human being consumes 100 times more air than food

Answer: (b)

Solution

Theoretical.

Question 59

Chemistry · Chemistry in Everyday Life · Single correct

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

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

Answer: (d)

Solution

Theoretical, NCERT based.

Question 60

Chemistry · Biomolecules · Numerical

Total number of tripeptides possible by mixing of valine and proline is

Answer: 8

Solution

The number of possible tripeptides with Val and Pro is $2^3$. (1) val – val – val (2) pro – pro – pro (3) val – pro – pro (4) pro – val – pro (5) val – val – pro (6) val – pro – val (7) pro – pro – val (8) pro – val – val

Maths

Question 61

Maths · Complex Numbers and Quadratic Equations · Single correct

The number of real solutions of the equation $$3 \left( x^2 + \frac{1}{x^2} \right) - 2 \left( x + \frac{1}{x} \right) + 5 = 0,$$ is

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

Answer: (b)

Solution

Given the equation: $$3 \left( x^2 + \frac{1}{x^2} \right) - 2 \left( x + \frac{1}{x} \right) + 5 = 0$$ Rewriting it as: $$3 \left[ \left( x + \frac{1}{x} \right)^2 - 2 \right] - 2 \left( x + \frac{1}{x} \right) + 5 = 0$$ Let $x + \frac{1}{x} = t$. Then the equation becomes: $$3t^2 - 2t - 1 = 0$$ Solving the quadratic equation: $$3t^2 - 3t + t - 1 = 0$$ Factorizing: $$3t(t - 1) + 1(t - 1) = 0$$ $$(t - 1)(3t + 1) = 0$$ Thus, $t = 1, -\frac{1}{3}$. For $x + \frac{1}{x} = 1, -\frac{1}{3}$, there is no solution.

Question 62

Maths · Complex Numbers and Quadratic Equations · Single correct

The value of $$\left( \frac{1 + \sin \frac{2\pi}{9} + i \cos \frac{2\pi}{9}}{1 + \sin \frac{2\pi}{9} - i \cos \frac{2\pi}{9}} \right)^3$$ is

  1. $-\frac{1}{2} \left( 1 - i \sqrt{3} \right)$
  2. $\frac{1}{2} \left( 1 - i \sqrt{3} \right)$
  3. $-\frac{1}{2} \left( \sqrt{3} - i \right)$
  4. $\frac{1}{2} \left( \sqrt{3} + i \right)$

Answer: (c)

Solution

Let $\sin \frac{2\pi}{9} + i \cos \frac{2\pi}{9} = z$. $$\left( \frac{1+z}{1+\frac{1}{z}} \right)^3 = \left( \frac{1+z}{1+\frac{1}{z}} \right)^3 = z^3$$ $$\Rightarrow \left( i \left( \cos \frac{2\pi}{9} - i \sin \frac{2\pi}{9} \right) \right)^3$$ $$= -i \left( \cos \frac{2\pi}{3} - i \sin \frac{2\pi}{3} \right) = -i \left( -\frac{1}{2} - i \frac{\sqrt{3}}{2} \right)$$ $$\Rightarrow \frac{-1}{2} (\sqrt{3} - i).$$

Question 63

Maths · Permutations and Combinations · Single correct

The number of integers, greater than 7000 that can be formed, using the digits 3, 5, 6, 7, 8 without repetition, is

  1. 120
  2. 168
  3. 220
  4. 48

Answer: (b)

Solution

Four digit numbers greater than 7000 $$= 2 \times 4 \times 3 \times 2 = 48$$ Five digit number $$= 5! = 120$$ Total number greater than 7000 $$= 120 + 48 = 168$$

Question 64

Maths · Sequences and Series · Numerical

If $\frac{1^3 + 2^3 + 3^3 + \ldots upto n terms}{1 \cdot 3 + 2 \cdot 5 + 3 \cdot 7 + \ldots upto n terms}$ = $\frac{9}{5}$, then the value of n is

Answer: 5

Solution

$1^3+2^3+3^3+\cdots+n^3=\left(\frac{n(n+1)}{2}\right)^2$ Now, $1\cdot3+2\cdot5+3\cdot7+\cdots+n$ terms $=\sum_{r=1}^{n}r(2r+1)$ $=\sum_{r=1}^{n}(2r^2+r)$ $=\frac{2\cdot n(n+1)(2n+1)}{6}+\frac{n(n+1)}{2}$ $=\frac{n(n+1)}{6}\Big(2(2n+1)+3\Big)$ $=\frac{n(n+1)}{6}(4n+5)$ If $\frac{n^2(n+1)^2}{4}=\frac{9}{5}\cdot\frac{n(n+1)}{6}(4n+5)$ then $\frac{n(n+1)}{2}=\frac{9(4n+5)}{15}$ $\Rightarrow 5n(n+1)=\frac{9(4n+5)}{3}$ $\Rightarrow 15n(n+1)=18(4n+5)$ $\Rightarrow 15n^2+15n=72n+90$ $\Rightarrow 15n^2-57n-90=0$ $\Rightarrow 5n^2-19n-30=0$ $\Rightarrow (n-5)(5n+6)=0$ $\Rightarrow n=5$ or $n=-\frac{6}{5}$ Since $n$ is positive, $\Rightarrow n=5$.

Question 65

Maths · Binomial Theorem · Single correct

If $({}^{30}C_{1})^2 + 2({}^{30}C_{2})^2 + 3({}^{30}C_{3})^2 + \ldots + 30({}^{30}C_{30})^2 = \frac{\alpha\;60!}{(30!)^2}$, then $\alpha$ is equal to

  1. 30
  2. 60
  3. 15
  4. 10

Answer: (c)

Solution

S = 0 $\cdot$ $({}^{30}C_{0})^2$ + 1 $\cdot$ $({}^{30}C_{1})^2$ + 2 $\cdot$ $({}^{30}C_{2})^2$ + $\ldots$ + 30 $\cdot$ $({}^{30}C_{30})^2$. S = 30 $\cdot$ $({}^{30}C_{0})^2$ + 29 $\cdot$ $({}^{30}C_{1})^2$ + 28 $\cdot$ $({}^{30}C_{2})^2$ + $\ldots$ + 0 $\cdot$ $({}^{30}C_{30})^2$. 2S = 30 $\cdot$ $\left( ({}^{30}C_{0})^2 + ({}^{30}C_{1})^2 + \ldots + ({}^{30}C_{30})^2 \right)$. S = 15 $\cdot$ ${}^{60}C_{30}$ = 15 $\cdot$ $\frac{60!}{(30!)^2}$. $\frac{15 \cdot 60!}{(30!)^2}$ = $\frac{\alpha \cdot 60!}{(30!)^2}$. $\Rightarrow$ $\alpha$ = 15.

Question 66

Maths · Binomial Theorem · Fill in the blank

Let the sum of the coefficients of the first three terms in the expansion of $$\left( x - \frac{3}{2x} \right)^n$$, $x \neq 0$, $n \in \mathbb{N}$, be 376. Then the coefficient of $x^4$ is ________.

Answer: 405

Solution

Given Binomial $\left( x - \frac{3}{x^2} \right)^n$, $x \neq 0$, $n \in \mathbb{N}$, Sum of coefficients of first three terms $$^nC_0 - ^nC_1 \cdot 3 + ^nC_2 \cdot 3^2 = 376$$ $$\Rightarrow 3n^2 - 5n - 250 = 0$$ $$\Rightarrow (n - 10)(3n + 25) = 0$$ $$\Rightarrow n = 10$$ Now general term $$^{10}C_r x^{10-r} \left( \frac{-3}{x^2} \right)^r$$ $$= ^{10}C_r x^{10-r} (-3)^r \cdot x^{-2r}$$ $$= ^{10}C_r (-3)^r \cdot x^{10-3r}$$ Coefficient of $x^4$ $\Rightarrow 10 - 3r = 4$ $$\Rightarrow r = 2$$ $$^{10}C_2 (-3)^2 = 405$$

Question 67

Maths · Trigonometric Functions · Numerical

\[ \text{Let } S=\left\{ \theta\in[0,2\pi): \tan(\pi\cos\theta)+\tan(\pi\sin\theta)=0 \right\}. \] \[ \text{Then } \sum_{\theta\in S} \sin^2\left(\theta+\frac{\pi}{4}\right) \text{ is equal to } \underline{\hspace{1cm}}. \]

Answer: 2

Solution

Given $\tan(\pi \cos \theta) + \tan(\pi \sin \theta) = 0$. This implies $\tan(\pi \cos \theta) = -\tan(\pi \sin \theta)$. Therefore, $\tan(\pi \cos \theta) = \tan(-\pi \sin \theta)$. Thus, $\pi \cos \theta = n\pi - \pi \sin \theta$. We have $\sin \theta + \cos \theta = n$ where $n \in \mathbb{I}$. Possible values are $n = 0, 1$ and $-1$ because $$-\sqrt{2} \leq \sin \theta + \cos \theta \leq \sqrt{2}$$ Now it gives $\theta \in \left\{ 0, \frac{\pi}{2}, \frac{3\pi}{4}, \frac{7\pi}{4}, \frac{3\pi}{2}, \pi \right\}$. So, $$\sum_{\theta \in S} \sin^2 \left( \theta + \frac{\pi}{4} \right) = 2(0) + 4 \left( \frac{1}{2} \right) = 2$$

Question 68

Maths · Straight Lines and Pair of Straight Lines · Numerical

The equations of the sides AB, BC and CA of a triangle ABC are: $2x + y = 0$, $x + py = 21a$, $(a \neq 0)$ and $x - y = 3$ respectively. Let $P (2, a)$ be the centroid of $\triangle ABC$. Then $(BC)^2$ is equal to

Answer: 122

Solution

Assume $B(\alpha, -2\alpha)$ and $C(\beta + 3, \beta)$. $$\frac{\alpha + \beta + 3 + 1}{3} = 2$$ also $$\frac{-2\alpha - 2 + \beta}{3} = a$$

Question 69

Maths · Conic Sections · Single correct

The locus of the mid points of the chords of the circle $C_1 : (x - 4)^2 + (y - 5)^2 = 4$ which subtend an angle $\theta_i$ at the centre of the circle $C_1$, is a circle of radius $r_i$. If $\theta_1 = \frac{\pi}{3}$, $\theta_3 = \frac{2\pi}{3}$ and $r_1^2 = r_2^2 + r_3^2$, then $\theta_2$ is equal to

  1. $\frac{\pi}{4}$
  2. $\frac{3\pi}{4}$
  3. $\frac{\pi}{6}$
  4. $\frac{\pi}{2}$

Answer: (d)

Solution

In $\triangle CPB$, $\($ $\cos$ $\frac{\theta}{2}$ = $\frac{PC}{2}$ $\Rightarrow$ PC = 2 $\cos$ $\frac{\theta}{2}$ $\)$ $\($ $\Rightarrow$ (h - 4)^2 + (k - 5)^2 = 4 $\cos$^2 $\frac{\theta}{2}$ $\)$ Now $\($ (x - 4)^2 + (y - 5)^2 = $\left$( 2 $\cos$ $\frac{\theta}{2}$ $\right$)^2 $\)$ $\($ $\Rightarrow$ r_1 = 2 $\cos$ $\frac{\pi}{6}$ = $\sqrt{3}$ $\)$ $\($ r_2 = 2 $\cos$ $\frac{\theta}{2}$ $\)$ $\($ r_3 = 2 $\cos$ $\frac{\pi}{3}$ = 1 $\)$ $\($ $\Rightarrow$ 5 = 3 + $\cos$ $\frac{\theta}{2}$ + 1 $\)$

Question 70

Maths · Conic Sections · Single correct

The equations of the sides AB and AC of a triangle ABC are ($\lambda$ + 1) x + $\lambda$ y = 4 and $\lambda$ x + (1 - $\lambda$) y + $\lambda$ = 0 respectively. Its vertex A is on the y-axis and its orthocentre is (1, 2). The length of the tangent from the point C to the part of the parabola $y^2$ = 6x in the first quadrant is

  1. $\sqrt{6}$
  2. $2\sqrt{2}$
  3. 2
  4. 4

Answer: (b)

Solution

AB: ($\lambda$ + 1)x + $\lambda$ y = 4 AC: $\lambda$ x + (1 - $\lambda$)y + $\lambda$ = 0 Vertex A is on y-axis $\Rightarrow$ x = 0 So y = $\frac{4}{\lambda}$, y = $\frac{\lambda}{\lambda - 1}$ $\Rightarrow$ $\frac{4}{\lambda}$ = $\frac{\lambda}{\lambda - 1}$ $\Rightarrow$ $\lambda$ = 2 AB: 3x + 2y = 4 AC: 2x - y + 2 = 0 $\Rightarrow$ A(0, 2) Let C($\alpha$, 2$\alpha$ + 2) Now (Slope of Altitude through C) $\left$(-$\frac{3}{2}$$\right$) = -1 $\left$($\frac{2\alpha}{\alpha - 1}$$\right$)$\left$(-$\frac{3}{2}$$\right$) = -1 $\Rightarrow$ $\alpha$ = -$\frac{1}{2}$ So C$\left$(-$\frac{1}{2}$, 1$\right$) Let Equation of tangent be y = mx + $\frac{\gamma}{2m}$

Question 71

Maths · Limits and Derivatives · Single correct

The set of all values of $a$ for which $$\lim_{{x \to a}} ([x - 5] - [2x + 2]) = 0,$$ where $[\infty]$ denotes the greater integer less than or equal to $\infty$ is equal to

  1. (-7.5, -6.5)
  2. (-7.5, -6.5]
  3. [-7.5, -6.5]
  4. [-7.5, -6.5)

Answer: (a)

Solution

Given $$\lim_{x \to a} ([x - 5] - [2x + 2]) = 0$$ $$\lim_{x \to a} ([x] - 5 - [2x] - 2) = 0$$ $$\lim_{x \to a} ([x] - [2x]) = 7$$ Let $[a] - [2a] = 7$. If $a \in \mathbb{I}$, then $a = -7$. If $a \notin \mathbb{I}$, then $a = I + f$. Now, $[a] - [2a] = 7$ implies $$-I - [2f] = 7$$ Case-I: $f \in \left(0, \frac{1}{2}\right)$ Then $2f \in (0, 1)$ $$-I = 7$$ Thus, $I = -7 \implies a \in (-7, -6.5)$ Case-II: $f \in \left(\frac{1}{2}, 1\right)$ Then $2f \in (1, 2)$ $$-I - 1 = 7$$ Thus, $I = -8 \implies a \in (-7.5, -7)$ Hence, $a \in (-7.5, -6.5)$.

Question 72

Maths · Mathematical Reasoning · Single correct

Let p and q be two statements. Then $\sim (p \land (p \Rightarrow \sim q))$ is equivalent to

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

Answer: (c)

Solution

We start with the expression $\sim (p \land (p \to \sim q))$. This is equivalent to $\sim p \lor \sim (\sim p \lor \sim q)$. Simplifying further, we get $\sim p \lor (p \land q)$. This can be rewritten as $(\sim p \lor p) \land (\sim p \lor q)$. Since $\sim p \lor p$ is a tautology, it simplifies to $t \land (\sim p \lor q)$. Finally, this reduces to $\sim p \lor q$.

Question 73

Maths · Statistics · Single correct

Let the six numbers $a_1, a_2, a_3, a_4, a_5, a_6$ be in A.P. and $a_1 + a_3 = 10$. If the mean of these six numbers is $\frac{19}{2}$ and their variance is $\sigma^2$, then $8\sigma^2$ is equal to

  1. 220
  2. 210
  3. 200
  4. 105

Answer: (b)

Solution

Given $a_1 + a_3 = 10 = a_1 + d \Rightarrow d = 5$. $a_1 + a_2 + a_3 + a_4 + a_5 + a_6 = 57$. Therefore, $$\frac{6}{2} [a_1 + a_6] = 57$$ This implies $a_1 + a_6 = 19$. Thus, $2a_1 + 5d = 19$ and $a_1 + d = 5$. Solving these, we get $a_1 = 2$, $d = 3$. The numbers are: $2, 5, 8, 11, 14, 17$. Variance $= \sigma^2 = mean of squares - square of mean$. $$= \frac{2^2 + 5^2 + 8^2 + (11)^2 + (14)^2 + (17)^2}{6} - \left(\frac{19}{2}\right)^2$$ $$= \frac{699}{6} - \frac{361}{4} = \frac{105}{4}$$ Finally, $8\sigma^2 = 210$.

Question 74

Maths · Relations and Functions · Fill in the blank

The minimum number of elements that must be added to the relation $R = \{(a, b), (b, c), (b, d)\}$ on the set $\{a, b, c, d\}$ so that it is an equivalence relation, is .

Answer: 13

Solution

Given $R = \{(a, b), (b, c), (b, d)\}$. In order to make it equivalence relation as per given set, $R$ must be $$\{(a, a), (b, b), (c, c), (d, d), (a, b), (b, a), (b, c), (c, b), (b, d), (d, b), (a, c), (a, d), (c, d), (d, c), (c, a), (d, a)\}$$ There already given so 13 more to be added.

Question 75

Maths · Matrices · Single correct

The number of square matrices of order 5 with entries from the set $\{$0, 1$\}$, such that the sum of all the elements in each row is 1 and the sum of all the elements in each column is also 1, is

  1. 225
  2. 120
  3. 150
  4. 125

Answer: (b)

Solution

In each row and each column exactly one is to be placed. Therefore, the number of such materials is $5 \times 4 \times 3 \times 2 \times 1 = 120$. Alternate: $$\begin{bmatrix} 0 & 0 & 1 & 0 & 0 \end{bmatrix} \rightarrow 5 ways$$ $$\begin{bmatrix} 0 & 1 & 0 & 0 & 0 \end{bmatrix} \rightarrow 4 ways$$ $$\begin{bmatrix} 0 & 0 & 0 & 1 & 0 \end{bmatrix} \rightarrow 3 ways$$ $$\begin{bmatrix} 0 & 0 & 0 & 0 & 1 \end{bmatrix} \rightarrow 2 ways$$ $$\begin{bmatrix} 1 & 0 & 0 & 0 & 0 \end{bmatrix} \rightarrow 1 way$$ Step-1: Select any 1 place for 1's in row 1. Automatically some column will get filled with 0's. Step-2: From next now select 1 place for 1's. Automatically some column will get filled with 0's. Each time one less place will be available for putting 1's. Repeat step-2 till last row. Required ways $= 5 \times 4 \times 3 \times 2 \times 1 = 120$ $3 \sqrt{3}$

Question 76

Maths · Matrices · Single correct

Let A be a 3 $\times$ 3 matrix such that $| adj ( adj(adj A) ) |$ = $12^4$. Then | $A^{-1}$ adj A | is equal to

  1. 2 $\sqrt{3}$
  2. $\sqrt{6}$
  3. 12
  4. 1

Answer: (a)

Solution

Given $|adj (adj (adj A))| = 12^4$. $$\Rightarrow |A|^{(n-1)^3} = 12^4$$ Given $n = 3$ $$\Rightarrow |A|^8 = 12^4$$ $$\Rightarrow |A|^2 = 12$$ $$|A| = 2\sqrt{3}$$ We are asked $$|A^{-1} \cdot adj A|$$ $$= |A^{-1}| \cdot |adj A|$$ $$= \frac{1}{|A|} \cdot |A|^{3-1}$$ $$= |A| = 2\sqrt{3}$$

Question 77

Maths · Determinants · Single correct

If the system of equations x + 2y + 3z = 3 4x + 3y - 4z = 4 8x + 4y - $\lambda$ z = 9 + $\mu$ has infinitely many solutions, then the ordered pair ($\lambda$, $\mu$) is equal to

  1. ( $\frac{72}{5}$, $\frac{21}{5}$ )
  2. ( $\frac{-72}{5}$, $\frac{-21}{5}$ )
  3. ( $\frac{72}{5}$, $\frac{-21}{5}$ )
  4. ( $\frac{-72}{5}$, $\frac{21}{5}$ )

Answer: (c)

Solution

Given the equations: $$x + 2y + 3z = 3 \ldots (i)$$ $$4x + 3y - 4z = 4 \ldots (ii)$$ $$8x + 4y - \lambda z = 9 + \mu \ldots (iii)$$ Multiply equation (i) by 4 and subtract equation (ii): $$5y + 16z = 8 \ldots (iv)$$ Multiply equation (ii) by 2 and subtract equation (iii): $$2y + (\lambda - 8)z = -1 - \mu \ldots (v)$$ Multiply equation (iv) by 2 and subtract equation (iii) multiplied by 5: $$(32 - 5(\lambda - 8))z = 16 - 5(-1 - \mu)$$ For infinite solutions: $$72 - 5\lambda = 0 \implies \lambda = \frac{72}{5}$$ Solve for $\mu$: $$21 + 5\mu = 0 \implies \mu = \frac{-21}{5}$$ Thus, $$\Rightarrow (\lambda, \mu) \equiv \left( \frac{72}{5}, \frac{-21}{5} \right)$$

Question 78

Maths · Relations and Functions · Single correct

If $f(x) = \frac{2^{2x}}{2^{2x} + 2}$, $x \in \mathbb{R}$, then $f\left(\frac{1}{2023}\right) + f\left(\frac{2}{2023}\right) + \ldots + f\left(\frac{2022}{2023}\right)$ is equal to

  1. 2011
  2. 1010
  3. 2010
  4. 1011

Answer: (d)

Solution

Given $f(x) = \frac{4^x}{4^x + 2}$. $f(x) + f(1-x) = \frac{4^x}{4^x + 2} + \frac{4^{1-x}}{4^{1-x} + 2}$ $$= \frac{4^x}{4^x + 2} + \frac{4}{4 + 2(4^x)}$$ $$= \frac{4^x}{4^x + 2} + \frac{2}{2 + 4^x}$$ $$= 1$$ Thus, $f(x) + f(1-x) = 1$. Now $f\left(\frac{1}{2023}\right) + f\left(\frac{2}{2023}\right) + f\left(\frac{3}{2023}\right) + \ldots + \ldots + f\left(1 - \frac{3}{2023}\right) + f\left(1 - \frac{2}{2023}\right) + f\left(1 - \frac{1}{2023}\right)$ Now the sum of terms equidistant from the beginning and end is 1. Sum $= 1 + 1 + 1 + \ldots + 1 \ (1011 times)$ $$= 1011$$

Question 79

Maths · Relations and Functions · Single correct

Let f(x) be a function such that f(x + y) = f(x) $\cdot$ f(y) for all x, y $\in$ $\mathbb{N}$. If f(1) = 3 and $\sum_{k=1}^{n}f(k)=3279$, then the value of n is

  1. 6
  2. 8
  3. 7
  4. 9

Answer: (c)

Solution

Given $f(x + y) = f(x) \cdot f(y)$ for all $x, y \in \mathbb{N}$, $f(1) = 3$. $f(2) = f^2(1) = 3^2$ $f(3) = f(1) f(2) = 3^3$ $f(4) = 3^4$ $f(k) = 3^k$ $$\sum_{k=1}^{n} f(k) = 3279$$ $f(1) + f(2) + f(3) + \ldots + f(k) = 3279$ $3 + 3^2 + 3^3 + \ldots + 3^k = 3279$ $$\frac{3(3^k - 1)}{3 - 1} = 3279$$ $$\frac{3^k - 1}{2} = 1093$$ $$3^k - 1 = 2186$$ $$3^k = 2187$$ $k = 7$

Question 80

Maths · Continuity and Differentiability · Single correct

If $f(x) = x^3 - x^2 f'(1) + x f''(2) - f'''(3)$, $x \in \mathbb{R}$, then

  1. $3f(1) + f(2) = f(3)$
  2. $f(3) - f(2) = f(1)$
  3. $2f(0) - f(1) + f(3) = f(2)$
  4. $f(1) + f(2) + f(3) = f(0)$

Answer: (c)

Solution

Given $f(x) = x^3 - x^2 f'(1) + x f''(2) - f'''(3)$, $x \in \mathbb{R}$. Let $f'(1) = a$, $f''(2) = b$, $f'''(3) = c$. Then, $$f(x) = x^3 - ax^2 + bx - c$$ Differentiating, $$f'(x) = 3x^2 - 2ax + b$$ $$f''(x) = 6x - 2a$$ $$f'''(x) = 6$$ Given $c = 6$, $a = 3$, $b = 6$, we have $$f(x) = x^3 - 3x^2 + 6x - 6$$ Calculating values, $$f(1) = -2, \ f(2) = 2, \ f(3) = 12, \ f(0) = -6$$ Finally, $$2f(0) - f(1) + f(3) = 2 = f(2)$$

Question 81

Maths · Integrals · Single correct

$\int_{\frac{3\sqrt{2}}{4}}^{\frac{3\sqrt{3}}{4}}\frac{48}{\sqrt{9-4x^2}}\,dx$ is equal to

  1. $\frac{\pi}{3}$
  2. $\frac{\pi}{2}$
  3. $\frac{\pi}{6}$
  4. $2\pi$

Answer: (d)

Solution

Given $$\int_{\frac{3\sqrt{2}}{4}}^{\frac{3\sqrt{3}}{4}} \frac{48}{\sqrt{9 - 4x^2}} \, dx$$. We have $$\int \frac{dx}{\sqrt{a^2 - x^2}} = \sin^{-1} \frac{x}{a} + C$$. Hence, $$\int_{\frac{3\sqrt{2}}{4}}^{\frac{3\sqrt{3}}{4}} \frac{48}{\sqrt{9 - 4x^2}} \, dx = \frac{48}{2} \left[ \sin^{-1} \frac{2x}{3} \right]_{\frac{3\sqrt{2}}{4}}^{\frac{3\sqrt{3}}{4}}$$ $$= 24 \times \left[ \sin^{-1} \left( \frac{2}{3} \times \frac{3\sqrt{3}}{4} \right) - \sin^{-1} \left( \frac{2}{3} \times \frac{3\sqrt{2}}{4} \right) \right]$$ $$= 24 \times \left[ \sin^{-1} \frac{\sqrt{3}}{2} - \sin^{-1} \frac{1}{\sqrt{2}} \right]$$ $$= 24 \times \left( \frac{\pi}{3} - \frac{\pi}{4} \right)$$ $$= 24 \times \frac{\pi}{12} = 2\pi$$

Question 82

Maths · Integrals · Fill in the blank

Let f be a differentiable function defined on $\left[ 0, \frac{\pi}{2} \right]$ such that $f(x) > 0$ and \[ f(x) + \int_{0}^{x} f(t) \sqrt{1 - (\log_e f(t))^2} \, dt = e, \quad \forall \, x \in \left[ 0, \frac{\pi}{2} \right]. \] Then $\left( 6 \log_e f \left( \frac{\pi}{6} \right) \right)^2$ is equal to _______.

Answer: 27

Solution

Given $$f(x) + \int_0^x f(t) \sqrt{1 - (\log_e f(t))^2} \, dt = e$$ This implies $$f(0) = e$$ Differentiating, we have $$f'(x) + f(x) \sqrt{1 - (\ln f(x))^2} = 0$$ Let $f(x) = y$. Then $$\frac{dy}{dx} = -y \sqrt{1 - (\ln y)^2}$$ Integrating both sides, $$\int \frac{dy}{y \sqrt{1 - (\ln y)^2}} = -\int dx$$ Put $\ln y = t$, then $$\int \frac{dt}{\sqrt{1 - t^2}} = -x + C$$ This gives $$\sin^{-1} t = -x + C \implies \sin^{-1} (\ln y) = -x + C$$ Thus, $$\sin^{-1} (\ln f(x)) = -x + C$$ Given $f(0) = e$, we have $$\frac{\pi}{2} = C$$ Therefore, $$\sin^{-1} (\ln f(x)) = -x + \frac{\pi}{2}$$ Evaluating at $x = \frac{\pi}{6}$, $$\sin^{-1} \left( \ln f \left( \frac{\pi}{6} \right) \right) = -\frac{\pi}{6} + \frac{\pi}{2}$$ This simplifies to $$\sin^{-1} \left( \ln f \left( \frac{\pi}{6} \right) \right) = \frac{\pi}{3}$$

Question 83

Maths · Applications of Integrals · Numerical

If the area of the region bounded by the curves $y^2 - 2y = -x$, $x + y = 0$ is $A$, then $8A$ is equal to

Answer: 36

Solution

Given $y^2 - 2y = -x$. This implies $y^2 - 2y + 1 = -x + 1$. Therefore, $(y - 1)^2 = -(x - 1)$. We have $y = -x$. Points of intersection are found by solving $x^2 + 2x = -x$, which gives $x^2 + 3x = 0$. Thus, $x = 0, -3$. The area $A$ is given by: $$A = \int_{0}^{3} (-y^2 + 2y + y) \, dy$$ Evaluating the integral: $$= \frac{3y^2}{2} - \frac{y^3}{3} \bigg|_{0}^{3} = \frac{9}{2}$$ Finally, $8A = 36$.

Question 84

Maths · Differential Equations · Single correct

Let $y = y(x)$ be the solution of the differential equation $(x^2 - 3y^2)dx + 3xy \, dy = 0$, $y(1) = 1$. Then $6y^2(e)$ is equal to

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

Answer: (c)

Solution

$(x^2 - 3y^2) \, dx + 3xy \, dy = 0$ $\frac{dy}{dx} = \frac{3y^2 - x^2}{3xy}$ $\implies \frac{dy}{dx} = \frac{y}{x} - \frac{1}{3} \frac{x}{y}$ ...(1) Put $y = vx$ $\frac{dy}{dx} = v + x \frac{dv}{dx}$ (1) $\implies v + x \frac{dv}{dx} = v - \frac{1}{3} \frac{1}{v}$ $\implies v \, dv = -\frac{1}{3x} \, dx$ Integrating both sides $\frac{v^2}{2} = -\frac{1}{3} \ln x + c$ $\implies \frac{y^2}{2x^2} = -\frac{1}{3} \ln x + c$ $y(1) = 1 \implies \frac{1}{2} = c$ $\implies \frac{y^2}{2x^2} = -\frac{1}{3} \ln x + \frac{1}{2}$ $y^2(x^2) = \frac{2}{3} x^2 \ln x^2 - e^2$

Question 85

Maths · Vector Algebra · Single correct

Let $\vec{\alpha} = 4\hat{i} + 3\hat{j} + 5\hat{k}$ and $\vec{\beta} = \hat{i} + 2\hat{j} - 4\hat{k}$. Let $\vec{\beta}_1$ be parallel to $\vec{\alpha}$ and $\vec{\beta}_2$ be perpendicular to $\vec{\alpha}$. If $\vec{\beta} = \vec{\beta}_1 + \vec{\beta}_2$, then the value of $5\vec{\beta}_2 \cdot (\hat{i} + \hat{j} + \hat{k})$ is

  1. 6
  2. 11
  3. 7
  4. 9

Answer: (c)

Solution

Let $\vec{\beta}_1 = \lambda \vec{\alpha}$. Now $\vec{\beta}_2 = \vec{\beta} - \vec{\beta}_1$. $$= (\hat{i} + 2\hat{j} - 4\hat{k}) - \lambda (4\hat{i} + 3\hat{j} + 5\hat{k})$$ $$= (1 - 4\lambda) \hat{i} + (2 - 3\lambda) \hat{j} - (5\lambda + 4) \hat{k}$$ $\vec{\beta}_2 \cdot \vec{\alpha} = 0$. $$\Rightarrow 4(1 - 4\lambda) + 3(2 - 3\lambda) - 5(5\lambda + 4) = 0$$ $$\Rightarrow 4 - 16\alpha + 6 - 9\lambda - 25\lambda - 20 = 0$$ $$\Rightarrow 50\lambda = -10$$ $$\Rightarrow \lambda = \frac{-1}{5}$$ $$\vec{\beta}_2 = \left( 1 + \frac{4}{5} \right) \hat{i} + \left( 2 + \frac{3}{5} \right) \hat{j} - (-1 + 4) \hat{k}$$ $$\vec{\beta}_2 = \frac{9}{5} \hat{i} + \frac{13}{5} \hat{j} - 3\hat{k}$$ $$5\vec{\beta}_2 = 9\hat{i} + 13\hat{j} - 15\hat{k}$$ $$5\vec{\beta}_2 \cdot (\hat{i} + \hat{j} + \hat{k}) = 9 + 13 - 15 = 7$$

Question 86

Maths · Vector Algebra · Fill in the blank

Let $\vec{a}=\hat{i}+2\hat{j}+\lambda\hat{k}$, $\vec{b}=3\hat{i}-5\hat{j}-\lambda\hat{k}$, $\vec{a}\cdot\vec{c}=7$, $2\vec{b}\cdot\vec{c}+43=0$, $\vec{a}\times\vec{c}=\vec{b}\times\vec{c}$. Then $|\vec{a}\cdot\vec{b}|$ is equal to

Answer: 8

Solution

Given $\mathbf{a} = \hat{i} + 2\hat{j} + \lambda \hat{k}$, $\mathbf{b} = 3\hat{i} - 5\hat{j} - \lambda \hat{k}$, $\mathbf{a} \cdot \mathbf{c} = 7$. $\mathbf{a} \times \mathbf{c} - \mathbf{b} \times \mathbf{c} = \mathbf{0}$, $$(\mathbf{a} - \mathbf{b}) \times \mathbf{c} = \mathbf{0} \Rightarrow (\mathbf{a} - \mathbf{b}) is paralleled to \mathbf{c}$$ $\mathbf{a} - \mathbf{b} = \mu \mathbf{c}$, where $\mu$ is a scalar $$-2\hat{i} + 7\hat{j} + 2\lambda \hat{k} = \mu \cdot \mathbf{c}$$ Now $\mathbf{a} \cdot \mathbf{c} = 7$ gives $2\lambda^2 + 12 = 7\mu$ And $\mathbf{b} \cdot \mathbf{c} = -\frac{43}{2}$ gives $4\lambda^2 + 82 = 43\mu$ $\mu = 2$ and $\lambda^2 = 1$ $$|\mathbf{a} \cdot \mathbf{b}| = 8$$

Question 87

Maths · Three Dimensional Geometry · Single correct

Let the plane containing the line of intersection of the planes P1: x + ($\lambda$ + 4)y + z = 1 and P2: 2x + y + z = 2 pass through the points (0, 1, 0) and (1, 0, 1). Then the distance of the point (2$\lambda$, $\lambda$, -$\lambda$) from the plane P2 is

  1. 5$\sqrt{6}$
  2. 4$\sqrt{6}$
  3. 2$\sqrt{6}$
  4. 3$\sqrt{6}$

Answer: (d)

Solution

Equation of plane passing through point of intersection of P1 and P2 $$P = P1 + kP2$$ $$\left( x + (\lambda + 4)y + z - 1 \right) + k \left( 2x + y + z - 2 \right) = 0$$ Passing through $(0, 1, 0)$ and $(1, 0, 1)$ $$(\lambda + 4 - 1) + k(1 - 2) = 0$$ $$(\lambda + 3) - k = 0 ....(1)$$ Also passing $(1, 0, 1)$ $$(1 + 1 - 1) + k(2 + 1 - 2) = 0$$ $$1 + k = 0$$ $$k = -1$$ put in (1) $$\lambda + 3 + 1 = 0$$ $$\lambda = -4$$ Then point $(2 \lambda, \lambda, -\lambda)$ $$(-8, -4, 4)$$ $$d = \frac{| -16 - 4 + 4 - 2 |}{\sqrt{6}}$$ $$d = \frac{18}{\sqrt{6}} \times \frac{\sqrt{6}}{\sqrt{6}} = 3 \sqrt{6}$$

Question 88

Maths · Three Dimensional Geometry · Single correct

If the foot of the perpendicular drawn from (1, 9, 7) to the line passing through the point (3, 2, 1) and parallel to the planes $x + 2y + z = 0$ and $3y - z = 3$ is $(\alpha, \beta, \gamma)$, then $\alpha + \beta + \gamma$ is equal to

  1. $-1$
  2. $3$
  3. $1$
  4. $5$

Answer: (d)

Solution

Direction ratio of line is $\($ $\begin{vmatrix}$ $\hat{i}$ & $\hat{j}$ & $\hat{k}$ $\\$ 1 & 2 & 1 $\\$ 0 & 3 & -1 $\end{vmatrix}$ $\)$. $\($ = $\hat{i}$(-5) - $\hat{j}$(-1) + $\hat{k}$(3) $\)$ $\($ = -5$\hat{i}$ + $\hat{j}$ + 3$\hat{k}$ $\)$ Point $\($ P(1, 9, 7) $\)$ $\($ M $\left$( -5$\lambda$ + 3, $\lambda$ + 2, 3$\lambda$ + 1 $\right$) $\)$ $\($ $\overline{\mathrm{PM}}$ $\perp$ (-5$\hat{i}$ + $\hat{j}$ + 3$\hat{k}$) $\)$ $\($ -5(-5$\lambda$ + 2) + ($\lambda$ - 7) + 3(3$\lambda$ - 6) = 0 $\)$ $\($ $\Rightarrow$ 25$\lambda$ + $\lambda$ + 9$\lambda$ - 10 - 7 - 18 = 0 $\)$ $\($ $\Rightarrow$ $\lambda$ = 1 $\)$ Point $\($ M = (-2, 3, 4) = ($\alpha$, $\beta$, $\gamma$) $\)$ $\($ $\alpha$ + $\beta$ + $\gamma$ = 5 $\)$

Question 89

Maths · Three Dimensional Geometry · Numerical

If the shortest between the lines \[ \frac{x + \sqrt{6}}{2} = \frac{y - \sqrt{6}}{3} = \frac{z - \sqrt{6}}{4}\] and \[\frac{x - \lambda}{3} = \frac{y - 2\sqrt{6}}{4} = \frac{z + 2\sqrt{6}}{5} \] is 6, then the square of sum of all possible values of $\lambda$ is

Answer: 384

Solution

Shortest distance between the lines $$\frac{x + \sqrt{6}}{2} = \frac{y - \sqrt{6}}{3} = \frac{z - \sqrt{6}}{4}$$ $$\frac{x - \lambda}{3} = \frac{y - 2\sqrt{6}}{4} = \frac{2 + 2\sqrt{6}}{5}$$ is 6. Vector along line of shortest distance $$\begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 2 & 3 & 4 \\ 3 & 4 & 5 \end{vmatrix}, \Rightarrow -\hat{i} + 2\hat{j} - \hat{k} (its magnitude is \sqrt{6} )$$ Now $$\frac{1}{\sqrt{6}} \begin{vmatrix} \sqrt{6} + \lambda & \sqrt{6} & -3\sqrt{6} \\ 2 & 3 & 4 \\ 3 & 4 & 5 \end{vmatrix} = \pm 6$$ $$\Rightarrow \lambda = -2\sqrt{6}, 10\sqrt{6}$$ So, square of sum of these values is 384.

Question 90

Maths · Conic Sections · Numerical

The urns A, B and C contain 4 red, 6 black; 5 red, 5 black and $\lambda$ red, 4 black balls respectively. One of the urns is selected at random and a ball is drawn. If the ball drawn is red and the probability that it is drawn from urn C is 0.4 then the square of the length of the side of the largest equilateral triangle, inscribed in the parabola $y^2 = \lambda x$ with one vertex at the vertex of the parabola is

Answer: 432

Solution

Given $m^2 + 2m - 3 = 0$. Solving for $m$, we get $m = 1, -3$. So the tangent which touches in the first quadrant at $T$ is $$T \equiv \left( \frac{a}{m^2}, \frac{2a}{m} \right)$$ $$\equiv \left( \frac{3}{2}, 3 \right)$$ Therefore, $CT = \sqrt{4 + 4} = 2\sqrt{2}$. Consider the urns: Urn A: Red 4, Black 6 Urn B: Red 5, Black 5 Urn C: Red $\lambda$, Black 4 The probability is given by: $$P\left( \frac{C}{R} \right) = \frac{P(C)P\left( \frac{R}{C} \right)}{P(A)P\left( \frac{R}{A} \right) + P(B)P\left( \frac{R}{B} \right) + P(C)P\left( \frac{R}{C} \right)}$$ Substituting the values: $$0.4 = \frac{\frac{1}{3} \times \frac{\lambda}{\lambda + 4}}{\frac{1}{3} \times \frac{4}{10} + \frac{1}{3} \times \frac{5}{10} + \frac{1}{3} \times \frac{\lambda}{\lambda + 4}}$$ Solving, we find $\lambda = 6$. For the tangent line, $\tan 30^\circ = 3t = \frac{3}{2}t^2$. Thus, $$\frac{1}{\sqrt{3}} = \frac{2}{t}$$