NEET (UG)

Practice Test 1 — Kinetic Theory of Gases

12 questions • 18 minutes • auto-graded with full solutions

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Section A — MCQ (Single Correct)

Question 1

The ideal gas equation per molecule is:

Solution: $PV = NkT$ with $k = R/N_A$.

Question 2

At constant temperature, $P \propto 1/V$ is:

Solution: Boyle's law.

Question 3

The kinetic-theory expression for pressure is:

Solution: $P = \tfrac{1}{3}\rho\,\overline{v^2}$.

Question 4

The rms speed of a gas at temperature $T$ is $v$. At $4T$ it becomes:

Solution: $v_{rms} \propto \sqrt{T}$; $\sqrt{4} = 2$.

Question 5

The average translational KE per molecule depends only on:

Solution: $\overline{E} = \tfrac{3}{2}kT$.

Question 6

For a monatomic gas, $C_V$ equals:

Solution: $C_V = \tfrac{f}{2}R = \tfrac{3}{2}R$ for $f = 3$.

Question 7

The ratio $\gamma$ for a diatomic gas is:

Solution: $\gamma = 1 + 2/5 = 7/5$.

Question 8

The mean free path is inversely proportional to:

Solution: $\lambda \propto 1/n$.

Section B — Assertion & Reason

Question 9

A: At the same temperature, hydrogen molecules move faster than oxygen molecules.
R: At a given temperature, all gas molecules have the same average translational kinetic energy.

Solution: Equal average KE means lighter hydrogen must move faster ($v \propto 1/\sqrt{M}$) — R explains A.

Question 10

A: The pressure of an ideal gas is proportional to the mean square speed of its molecules.
R: Gas pressure arises from momentum transferred by molecules colliding with the walls.

Solution: $P = \tfrac{1}{3}\rho\,\overline{v^2}$ follows from wall collisions transferring momentum — R explains A.

Question 11

A: The internal energy of an ideal gas depends only on its temperature.
R: An ideal gas has no intermolecular potential energy, so its energy is purely kinetic.

Solution: With no intermolecular forces, energy is kinetic and set by $T$ alone — R explains A.

Question 12

A: The mean free path of a gas increases when its pressure is raised at constant temperature.
R: The mean free path is inversely proportional to the number density of molecules.

Solution: Raising pressure raises $n$, so $\lambda$ decreases — A is false; R is a true statement.