NEET Physics Kinetic Theory MCQs Set A

Question. Boyle's law is applicable for an
(a) isothermal process
(b) adiabatic process
(c) None of these
(d) isochoric process

Answer: A

Question. An inflated rubber balloon contains one mole of an ideal gas, has a pressure p, volume V and temperature T. If the temperature rises to 1.1 T, and the volume is increased to 1.05 V, the final pressure will be
(a) between p and 1.1
(b) 1.1 p
(c) less than p
(d) p

Answer: A

Question. The mean free path of molecules of a gas, (radius ‘r’) is inversely proportional to :
(a) r²
(b) r³
(c) r
(d) None of these

Answer: A

Question. Assertion : Mean free path of a gas molecules varies inversely as density of the gas.
Reason : Mean free path varies inversely as pressure of the gas
(a) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
(c) If Assertion is correct but Reason is incorrect
(d) If both the Assertion and Reason are incorrect

Answer: A

Question.  Two vessels separately contain two ideal gases A and B at the same temperature. The pressure of A being twice that of B. Under such conditions, the density of A is found to be 1.5 times the density of B. The ratio of molecular weight of A and B is :
(a) 3/4
(b) 2
(c) 1/2
(d) 2/3

Answer: A

Question.  A vessel of volume 20L contains a mixture of hydrogen and helium at temperature of 27°C and pressure 2 atm. The mass of mixture is 5g. Assuming the gases to be ideal, the ratio of mass of hydrogen to that of helium in the given mixture will be
(a) 2 : 5
(b) 1 : 2
(c) 2 : 1
(d) 2 : 3

Answer: A

Question. Assertion : One mole of any substance at any temperature or volume always contains 6.02 × 1023 molecules.
Reason : One mole of a substance always refers to S.T.P. conditions
(a) If Assertion is correct but Reason is incorrect.
(b) If both the Assertion and Reason are incorrect
(c) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
(d) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.

Answer: A

Question. A gas mixture consists of 2 moles of O₂ and 4 moles of Ar at temperature T. Neglecting all vibrational modes, the total internal energy of the system is :
(a) 11 RT
(b) 4 RT
(c) 9 RT
(d) 15 RT

Answer: A

Question. If the root mean square velocity of the molecules of hydrogen at NTP is 1.84 km/s. Calculate the root mean square velocity of oxygen molecule at NTP, molecular weight of hydrogen and oxygen are 2 and 32 respectively
(a) 0.47 km/sec
(b) 0.94 km/s
(c) 1.47 km/sec
(d) 1.84 km/s

Answer: A

Question. Assertion : Air pressure in a car tyre increases during driving.
Reason : Absolute zero temperature is not zero energy temperature.
(a) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
(b) If Assertion is correct but Reason is incorrect
(c) If both the Assertion and Reason are incorrect
(d) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion

Answer: A

Question.  Five gas molecules chosen at random are found to have speeds of 500, 600, 700, 800 and 900 m/s:
(a) The root mean square speed is 14 m/s higher than the average speed.
(b) The root mean square speed is 14 m/s lower than the average speed
(c) The root mean square speed is Ö14 m/s higher than the average speed
(d) The root mean square speed and the average speed are the same

Answer: A

Question.  At what temperature will the rms speed of oxygen molecules become just sufficient for escaping from the Earth’s atmosphere?
(Given : Mass of oxygen molecule (m) = 2.76 × 10^–26 kg Boltzmann’s constant k_B = 1.38 × 10^–23 JK^–1)
(a) 8.360 × 10⁴ K
(b) 5.016 × 10⁴ K
(c) 2.508 × 10⁴ K
(d) 1.254 × 10⁴ K

Answer: A

Question. Assertion : Each vibrational mode gives two degrees of freedom.
Reason : By law of equipartition of energy, the energy for each degree of freedom in thermal equilibrium is 2k_B T.
(a) Assertion is correct, reason is incorrect
(b) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(c) Assertion is incorrect, reason is correct
(d) Assertion is correct, reason is correct; reason is not a correct explanation for assertion

Answer: A

Question. Two moles of an ideal monoatomic gas occupies a volume V at 27°C. The gas expands adiabatically to a volume 2 V. Calculate (i) the final temperature of the gas and (ii) change in its internal energy.
(a) (i)189 K (ii) –2.7 kJ
(b) (i) 189 K (ii) 2.7 kJ
(c) (i)195 K (ii) –2.7 kJ
(d) (i)195 K (ii) 2.7 kJ

Answer: A

Question. The mass of H₂ molecule is 3.32 × 10^–24 g. If 10²³ hydrogen molecules per second strike 2 cm² of wall at an angle of 45^o with the normal, while moving with a speed of 10⁵ cm/s, the pressure exterted on the wall is nearly.
(a) 2350 N/m²
(b) 1660 N/m²
(c) 3320 N/m²
(d) 1350 N/m²

Answer: A

Question. By what percentage should the pressure of a given mass of a gas be increased so as to decrease its volume by 10% at a constant temperature?
(a) 11.1 %
(b) 10.1 %
(c) 9.1 %
(d) 8.1 %

Answer: A

Question. A closed hollow insulated cylinder is filled with gas at 0°C and also contains an insulated piston of negligible weight and negligible thickness at the middle point. The gas on one side of the piston is heated to 100°C. If the piston moves 5 cm, the length of the hollow cylinder is
(a) 64.6 cm
(b) 38.6 cm
(c) 27.3 cm
(d) 13.65 cm

Answer: A

Question.  Air is filled at 60°C in a vessel of open mouth. The vessel is heated to a temperature T so that 1/4th part of air escapes. Assuming the volume of vessel remaining constant, the value of T is
(a) 171°C
(b) 333°C
(c) 444°C
(d) 80°C

Answer: A

Question.  1 mole of a monatomic and 2 mole of diatomic gas are mixed, now the resulting gas is taken through a process in which molar heat capacity was found 3R. Polytropic constant in the process is
(a) –1/5
(b) 2/5
(c) 1/5
(d) None of these

Answer: A

Question.  The density of a gas is 6 × 10^–2 kg/m³ and the root mean square velocity of the gas molecules is 500 m/s. The pressure exerted by the gas on the walls of the vessel is
(a) 5×10³N / m²
(b) 0.83×10^–4 N / m²
(c) 1.2×10^–4N / m²
(d) 30N / m²

Answer: A

Question. The density of air at pressure of 10⁵ Nm^–2 is 1.2 kg m^–3. Under these conditions, the root mean square velocity of the air molecules in ms–1 is
(a) 500
(b) 1000
(c) 1500
(d) 3000

Answer: A