Kinetic TheoryNEET MCQs with solutions
Kinetic Theory covers the kinetic theory of gases, ideal gas equation, RMS/mean/most probable speeds, degrees of freedom, law of equipartition of energy and mean free path. NEET tests speed calculations, degrees of freedom for different molecules and the relationship between Cₚ and Cᵥ (γ = Cₚ/Cᵥ).
- Class
- 11 Physics
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- 24 questions
- In the RankUp app
- 491 questions
- ELITE questions
- 181
- NCERT topics
- 12
Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Grand Test
A monoatomic ideal gas expands isothermally. Which quantity remains constant throughout the process?
Not quite — the answer is C.
In an isothermal process T is constant. Average translational KE per molecule = (3/2)kT depends only on T, so it stays constant. Pressure falls, volume rises, and collision frequency drops as expansion occurs.
Q2Grand Test
The pressure exerted by an ideal gas is due to:
Not quite — the answer is B.
Pressure equals force per unit area at the wall. Each elastic collision transfers momentum to the wall; the rate of momentum transfer per unit area is the pressure. Gravity and intermolecular forces are neglected in ideal gas assumptions.
Q3Mixed Revision
Which of the following quantities depends only on the absolute temperature for an ideal gas?
Not quite — the answer is C.
Average translational KE per molecule = (3/2)kT depends only on T. Pressure depends on T, n, V; volume depends on T, n, P; density depends on both P and T.
Q4Mixed Revision
The ratio of rms speeds of hydrogen (M = 2 g/mol) and oxygen (M = 32 g/mol) at the same temperature is:
Not quite — the answer is B.
v_rms ∝ 1/√M. v_H2/v_O2 = √(32/2) = √16 = 4. So v_H2 : v_O2 = 4:1. Option A arises from inverting the ratio; Option C from using M directly instead of √M.
Q5Kinetic Theory of an Ideal Gas
According to the kinetic theory of gases, an ideal gas consists of a very large number of molecules which are:
Not quite — the answer is C.
A fundamental postulate: gas molecules are in continuous random motion in all directions. Option A is wrong — molecules move between collisions too. Option B is wrong — molecular speeds are distributed over a range, not equal for all.
Q6Kinetic Theory of an Ideal Gas
Which one of the following is NOT an assumption of the kinetic theory of an ideal gas?
Not quite — the answer is A.
Ideal gas molecules are assumed to exert no intermolecular forces except during the brief instant of collision. Assuming strong attractive forces throughout motion directly violates this core postulate and would describe a real gas, not an ideal one.
Q7Behaviour of Gases
A gas expands to fill the entire vessel because:
Not quite — the answer is B.
Gas molecules move randomly in all directions with negligible intermolecular attractive forces, spreading out to occupy the entire available volume uniformly. Attraction or infinite energy plays no role.
Q8Behaviour of Gases
Which property of gases is mainly responsible for their ability to be compressed easily?
Not quite — the answer is C.
Gases have very large empty spaces between molecules. When pressure is applied, molecules are pushed into this empty space, making gases highly compressible. Solids and liquids with minimal spacing resist compression.
Q9Pressure of an Ideal Gas
The pressure exerted by an ideal gas on the walls of its container is due to:
Not quite — the answer is C.
Pressure arises from continuous elastic collisions of gas molecules with container walls, transferring momentum. Attraction plays no role in ideal gas model.
Q10Pressure of an Ideal Gas
For an ideal gas at constant density, pressure is directly proportional to:
Not quite — the answer is B.
From P = (1/3) x rho x c_rms^2, pressure is proportional to mean square speed at constant density. Average speed (option C) is a common confusion — rms speed, not mean speed, appears in the formula.
Q11Law of Equipartition of Energy
According to the law of equipartition of energy, each active degree of freedom contributes an average energy of:
Not quite — the answer is A.
Equipartition theorem assigns (1/2)kT per active quadratic DOF per molecule. Option B (kT) is the trap — it equals the total for a 2-DOF system, not one DOF.
Q12Law of Equipartition of Energy
A monoatomic ideal gas has 3 active degrees of freedom. The average energy per molecule is:
Not quite — the answer is B.
Average energy = (f/2)kT = (3/2)kT for monoatomic gas (f=3). Option C is the trap — it applies to rigid diatomic (f=5), not monoatomic.
467 more questions on this chapter are waiting in the app
Every one with a detailed explanation, plus flashcards and chapter tests.
Get RankUp on Google PlayQ13Mean Free Path
Mean free path of a gas molecule is defined as the:
Not quite — the answer is B.
Mean free path is the average distance a molecule travels between two successive collisions. It is a property of individual molecular motion, not of the bulk gas.
Q14Mean Free Path
The SI unit of mean free path is:
Not quite — the answer is C.
Mean free path is a distance — the average length between successive collisions — so its SI unit is the metre (m). It is not a rate (s) or a cross-section (m squared).
Q15Molecular Nature of Matter
According to the molecular theory of matter, which statement best explains why solids retain a definite shape?
Not quite — the answer is B.
In solids, molecules vibrate about fixed mean positions but cannot change relative positions. Strong intermolecular forces prevent displacement, giving solids a definite rigid shape. Molecules are never at complete rest.
Q16Molecular Nature of Matter
Brownian motion is primarily evidence for which property of matter?
Not quite — the answer is D.
Random zig-zag motion of suspended particles results from continuous unequal bombardment by rapidly moving surrounding molecules, directly evidencing continuous molecular motion in fluids.
Q17Specific Heat Capacities of Gases
The molar specific heat at constant volume (Cv) of a rigid diatomic ideal gas is:
Not quite — the answer is C.
Rigid diatomic gas has f=5, so Cv=(f/2)R=(5/2)R. Monoatomic Cv=3R/2 is wrong; 7R/2 is Cp of rigid diatomic, not Cv.
Q18Specific Heat Capacities of Gases
The molar specific heat at constant pressure (Cp) of a rigid diatomic ideal gas is:
Not quite — the answer is D.
Rigid diatomic Cv=5R/2. By Mayer's relation, Cp=Cv+R=5R/2+R=7R/2. Option B is Cv, not Cp — the most common error here.
Q19Kinetic Interpretation of Temperature
According to the law of equipartition of energy, the average energy associated with each degree of freedom of a molecule at absolute temperature T is:
Not quite — the answer is D.
The law of equipartition assigns (1/2)kT of average energy to each degree of freedom. For a monatomic gas with 3 translational degrees, total average KE = 3 x (1/2)kT = (3/2)kT.
Q20Kinetic Interpretation of Temperature
Two different ideal gases are at the same absolute temperature. Which quantity is the same for each molecule of both gases?
Not quite — the answer is C.
At the same temperature, every ideal gas molecule has average translational kinetic energy = (3/2)kT, irrespective of molecular mass. rms speed differs because it depends on molar mass.
Q21Degrees of Freedom
For a monoatomic ideal gas, the number of degrees of freedom per molecule is:
Not quite — the answer is B.
A monoatomic molecule translates along three mutually perpendicular axes. It has no rotational or vibrational contribution at any temperature. Hence degrees of freedom per molecule = 3.
Q22Degrees of Freedom
A rigid diatomic gas molecule at ordinary temperature possesses how many active degrees of freedom?
Not quite — the answer is D.
A rigid diatomic molecule has 3 translational and 2 rotational degrees of freedom. Vibrational modes are frozen at ordinary temperatures. Total active DOF = 5. Option B (6) traps students who add one vibrational mode incorrectly.
Q23NCERT Summary & Key Concepts
According to NCERT, which assumption is made about the size of molecules in an ideal gas?
Not quite — the answer is A.
Ideal gas molecules are treated as point masses whose own volume is negligible compared with the container volume. Options B and D introduce false assumptions not part of kinetic theory.
Q24NCERT Summary & Key Concepts
Which one of the following statements is NOT an assumption of the kinetic theory of an ideal gas?
Not quite — the answer is D.
Elastic collisions conserve kinetic energy, so molecules do NOT lose energy after collision. Options A, B, and C are all standard kinetic theory assumptions stated in NCERT.
ELITE question · AIR under 50 level
This chapter has 181 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Kinetic Theory Facts
Quick revision: most questions in this chapter test these facts.
| Concept | Key Formula |
|---|---|
| Ideal gas equation | PV = nRT; R = 8.314 J mol⁻¹ K⁻¹ |
| RMS speed | v_rms = √(3RT/M) = √(3kT/m) |
| Mean speed | v_avg = √(8RT/πM); v_avg < v_rms |
| Most probable speed | v_mp = √(2RT/M); v_mp < v_avg < v_rms |
| Degrees of freedom | Mono: 3 (trans); Di: 5 (3 trans + 2 rot); Poly: 6–7 |
| γ = Cₚ/Cᵥ | Mono: 5/3; Di: 7/5; γ = 1 + 2/f (f = degrees of freedom) |
What the app covers in this chapter
491 questions in total, each with a detailed explanation.
| Grand Test | 57 |
| Mixed Revision | 57 |
| Kinetic Theory of an Ideal Gas | 43 |
| Behaviour of Gases | 40 |
| Pressure of an Ideal Gas | 40 |
| Law of Equipartition of Energy | 40 |
| Mean Free Path | 40 |
| Molecular Nature of Matter | 39 |
| Specific Heat Capacities of Gases | 39 |
| Kinetic Interpretation of Temperature | 38 |
| Degrees of Freedom | 38 |
| NCERT Summary & Key Concepts | 20 |
Questions students ask
Is Kinetic Theory important for NEET?
Yes — RMS speed, degrees of freedom and γ values are tested regularly. Questions are mostly formula-based and quick to solve.
Which topics should I revise first?
Master the three molecular speeds (v_mp < v_avg < v_rms) and their formulas, degrees of freedom for mono/di/polyatomic gases, γ values, and the law of equipartition of energy.
How many questions from this chapter are on RankUp?
The RankUp app has 491 questions on Kinetic Theory, including 181 ELITE questions. Every question has a detailed explanation.
