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NEET Physics: Kinetic Theory of Gases Practice Questions

12 free multiple-choice questions on Kinetic Theory of Gases for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. Which of the following is NOT an assumption made in the Kinetic Theory of Gases?

    • AThe molecules are in continuous random motion
    • BThe intermolecular forces of attraction between molecules are significant
    • CCollisions between molecules are perfectly elastic
    • DThe gas molecules are point masses
    Show answer & explanation

    Correct answer: B — The intermolecular forces of attraction between molecules are significant

    The kinetic theory assumes that intermolecular forces of attraction between molecules are negligible (or zero) for the motion to be treated classically. Significant forces would lead to more complex interactions than assumed for ideal gases.

  2. Q2. The work done in compressing a gas is directly proportional to the change in:

    • AInternal energy and heat.
    • BMass and velocity.
    • CPressure and volume.
    • DTemperature and pressure.
    Show answer & explanation

    Correct answer: C — Pressure and volume.

    Work done in a volume change is fundamentally defined by the change in pressure and volume (W = ∫ P dV). Compression involves decreasing volume, which results in a corresponding change in pressure and volume over that path.

  3. Q3. The rotational degrees of freedom for a linear molecule are:

    • A1
    • B2
    • C4
    • D3
    Show answer & explanation

    Correct answer: B — 2

    A linear molecule can rotate about two axes perpendicular to the molecular axis, giving 2 rotational degrees of freedom.

  4. Q4. In the context of kinetic theory, what physical motion corresponds to the vibrational degrees of freedom of a gas molecule?

    • AMovement in the plane of rotation
    • BMovement along the bond axis
    • CMovement perpendicular to the plane of rotation
    • DRotation around the bond axis
    Show answer & explanation

    Correct answer: B — Movement along the bond axis

    Vibrational degrees of freedom represent the stretching and compression of the intramolecular bonds along the molecular axis.

  5. Q5. Which assumption is necessary to state that the molecules of an ideal gas can be considered as moving randomly throughout the container?

    • AThe molecules are moving with uniform speed
    • BThe molecules are moving in straight lines
    • CThe molecules move in random and rapid collisions
    • DThe molecules maintain a fixed average velocity
    Show answer & explanation

    Correct answer: C — The molecules move in random and rapid collisions

    The assumption of random motion ensures that the average motion observed is uniform across the container, leading to thermodynamic equilibrium.

  6. Q6. If N_A is the number of particles in one mole, what does a quantity of 1 mole represent?

    • AThe total mass of the substance
    • BThe total number of particles of that substance
    • CThe total volume occupied by the substance
    • DThe total energy of the substance
    Show answer & explanation

    Correct answer: B — The total number of particles of that substance

    One mole represents a specific macroscopic amount of matter, defined by the number of particles (6.022 × 10²³) present in that amount.

  7. Q7. The assumption that gas molecules collide elastically with each other is important because it implies which physical concept?

    • AThe gas is an ideal gas.
    • BThe pressure exerted by the gas is independent of temperature.
    • CThe total kinetic energy of the gas remains constant during collisions.
    • DThe molecules possess zero potential energy.
    Show answer & explanation

    Correct answer: C — The total kinetic energy of the gas remains constant during collisions.

    Elastic collisions mean that the total kinetic energy of the system is conserved during the collisions, which is a key premise for deriving the kinetic theory equations.

  8. Q8. In the context of the Kinetic Theory of Gases, what property is assumed to be negligible regarding the forces of attraction or repulsion between the molecules?

    • AThe energy of translation.
    • BThe force of random motion.
    • CThe kinetic energy of the walls of the container.
    • DThe intermolecular forces of attraction/repulsion.
    Show answer & explanation

    Correct answer: D — The intermolecular forces of attraction/repulsion.

    A key assumption in KTG is that the intermolecular forces (attraction or repulsion) between gas molecules are negligible, except during instantaneous collisions.

  9. Q9. For a process where work is done on an ideal gas, the change in internal energy (ΔU) is related to the work done (W) and the change in heat (Q) by which thermodynamic principle?

    • AZeroth Law of Thermodynamics
    • BSecond Law of Thermodynamics
    • CThird Law of Thermodynamics
    • DFirst Law of Thermodynamics
    Show answer & explanation

    Correct answer: D — First Law of Thermodynamics

    The First Law of Thermodynamics states that the change in internal energy of a system is equal to the heat supplied to the system minus the work done by the system (ΔU = Q - W). If work is done *on* the gas, W is positive when considering the system's change, or ΔU = Q + W depending on the sign convention; the fundamental relationship is the First Law.

  10. Q10. When considering a gas mixture containing both monatomic and diatomic molecules, how is the total internal energy of the mixture determined based on the equipartition theorem?

    • AIt depends on the sum of the translational and rotational degrees of freedom of all molecules.
    • BIt depends only on the translational energy of the diatomic molecules.
    • CIt depends only on the total volume of the mixture.
    • DIt depends only on the difference between the average speeds of the two types of molecules.
    Show answer & explanation

    Correct answer: A — It depends on the sum of the translational and rotational degrees of freedom of all molecules.

    The internal energy of the mixture is the sum of the internal energies contributed by each type of molecule. Since energy is distributed across all translational and rotational degrees of freedom, the total internal energy depends on the combined degrees of freedom of all molecules present.

  11. Q11. Which property of the gas molecules primarily determines their root mean square speed?

    • AThe pressure exerted by the gas
    • BThe volume occupied by the gas
    • CThe density of the gas
    • DThe mass of the gas molecules
    Show answer & explanation

    Correct answer: D — The mass of the gas molecules

    The vᵣₘₛ is dependent on the average kinetic energy, which is determined by the translational kinetic energy of the molecules, which depends on their mass and the temperature.

  12. Q12. One mole of any ideal gas occupies a volume of approximately:

    • A100 L
    • B22.4 L
    • C11.2 L
    • D22.4 m³
    Show answer & explanation

    Correct answer: B — 22.4 L

    At Standard Temperature and Pressure (STP), one mole of any ideal gas occupies a volume of 22.4 Liters.

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