NEET PhysicsUpdated 19 Oct 2026

Kinetic Theory of Gases: NEET PYQs and weightage

Kinetic Theory of Gases carries 3.6 of 100 Physics marks in NEET by past-paper share: 27 of the 758 tagged NEET Physics PYQs in the ViJEEta bank (NEET 2013–2026). It ranks 11 of 30 Physics chapters.

Take the 25-question Kinetic Theory of Gases test Formula sheet ↓All NEET Physics chapters

3.6/100 Weight in Physics

Exam importance (3/5, by past-paper share)

27 NEET PYQs

223 Practice questions

201 With measured difficulty

How the weight is computed: this chapter's tagged NEET PYQs divided by all tagged NEET Physics PYQs in the bank (27 of 758), times 100, with repeated questions counted once. The bank does not store the year of each NEET question, so none is printed. Computed from the bank at build time. Updated 19 Oct 2026.

Kinetic Theory of Gases: formula sheet for NEET

14 formulas, each with when to use it. Copy it onto one page of your notebook: that page is this chapter's handbook.

Ideal gas equation
$P V = μ R T = N k_{B} T$
$so P = n k_{B} T (n = molecules per m^{3}; R = 8.314 J mol^{- 1} K^{- 1}, k_{B} = R / N_{A} = 1.38 \times 1 0^{- 23} J K^{- 1})$
Use it when: you need $P$ , $V$ , $T$ , moles or the number of molecules of a gas sample.
Density form
$P = \frac{ρR T}{M _{0}} (M_{0} = molar mass in kg/mol)$
Use it when: the question gives density instead of volume or moles.
Kinetic theory pressure
$P = \frac{1}{3} nm ⟨ v^{2} ⟩$
$P V = \frac{2}{3} E (E = total translational KE)$
Use it when: you need to link pressure to molecular speed or to translational KE.
Average KE per molecule
$\frac{1}{2} m ⟨ v^{2} ⟩ = \frac{3}{2} k_{B} T$
Use it when: you are comparing KE of gases at the same $T$ . It depends only on $T$ , not on the gas.
RMS speed
$v_{r m s} = ⟨ v^{2} ⟩ = \frac{3 k _{B} T}{m} = \frac{3 R T}{M _{0}}$
Use it when: you need a speed from temperature, or a speed ratio at the same $T$ ( $v_{r m s} \propto 1/ M_{0}$ ).
Average and most probable speed
$v_{a v g} = \frac{8 k _{B} T}{π m}$
$v_{m p} = \frac{2 k _{B} T}{m}$
$so v_{m p} : v_{a v g} : v_{r m s} \approx 1.41 : 1.60 : 1.73$
Use it when: the question asks which speed is largest or for the ratio between the three.
Dalton's law
$P = P_{1} + P_{2} + \dots$
$P_{1} = \frac{μ _{1} R T}{V}$
Use it when: a mixture of non-reacting gases shares one vessel.
Equipartition
$\frac{1}{2} k_{B} T (per translational or rotational degree of freedom)$
$k_{B} T (per vibrational mode: KE + PE)$
Use it when: you need the energy per molecule for a given type of molecule.
Change in internal energy
$Δ U = μ C_{v} Δ T (U of an ideal gas depends on T only)$
Use it when: $T$ changes in any process, not just at constant volume.
Relation between molar specific heats
$C_{p} - C_{v} = R (ideal gas)$
Use it when: you know one molar specific heat and need the other. It holds for every ideal gas.
Monatomic gas
$U = \frac{3}{2} R T (per mole)$
$C_{v} = \frac{3}{2} R$
$C_{p} = \frac{5}{2} R$
$γ = \frac{5}{3}$
Use it when: the gas is He, Ne, Ar and similar.
Diatomic gas (rigid)
$C_{v} = \frac{5}{2} R$
$C_{p} = \frac{7}{2} R$
$γ = \frac{7}{5} .$
$With one vibrational mode: C_{v} = \frac{7}{2} R$
$C_{p} = \frac{9}{2} R$
$γ = \frac{9}{7}$
Use it when: the gas is $O_{2}$ , $N_{2}$ and similar. Treat it as rigid unless vibration is mentioned.
Polyatomic gas (f vibrational modes)
$C_{v} = (3 + f) R$
$C_{p} = (4 + f) R$
$γ = \frac{4 + f}{3 + f}$
Use it when: the molecule is non-linear with 3 translational and 3 rotational degrees of freedom.
Mean free path
$l = \frac{1}{2 nπ d ^{2}} (d = diameter of the molecule, not radius)$
Use it when: you are asked the average distance between collisions, or how $l$ changes with $n$ .

Trap

In v_rms = √(3RT/M₀), T must be in kelvin and M₀ in kg/mol (O₂ is 0.032, not 32). Using grams makes v_rms √1000 ≈ 31.6 times too small; using °C instead of kelvin also gives a wrong answer.

How does NEET ask Kinetic Theory of Gases?

8 real previous-year questions from this chapter, as printed in the paper, each with its worked solution. Answer the first one here with no sign-in.

Q1PhysicsNEET UG PYQMean Free Path

Try right here · No sign-in

The mean free path for a gas, with molecular diameter d and number density n can be expressed as:

Answer key (D) & worked solution

Correct answer: Option D

The mean free path for gas is given by

λ = \frac{1}{2 π n d ^{2}}

Q2PhysicsNEET UG PYQLaw of Equipartition of Energy and Specific Heat Capacity

A gas mixture consists of 2 mole of O

_{2}

and 4 mole of Ar at temperature T kelvin. Neglecting all vibrational modes, the total internal energy of the system is

A9RT

B11RT

C4RT

D15RT

Answer key (B) & worked solution

Correct answer: Option B

U = n_{1} \frac{f _{1}}{2} R T + n_{2} \frac{f _{2}}{2} R T

= 2 \times \frac{5}{2} R T + 4 \times \frac{3}{2} R T

= 5 R T + 6 R T

U = 11 R T

Q3PhysicsNEET UG PYQBehaviour of Gases

A given sample of an ideal gas occupies a volume V at a pressure P and absolute temperature T. The mass of each molecule of the gas is m. Which of the following gives the density of the gas?(k is boltzmanm constant)

\frac{P m}{k T}

\frac{P}{k T V}

mk T

\frac{P}{k T}

Answer key (A) & worked solution

Correct answer: Option A

\frac{P}{ρ} = \frac{R T}{M _{w}}

(Gas equation)

\Rightarrow ρ = \frac{P M _{w}}{R T} = \frac{P \times ( m N _{A} )}{k N _{A} T} = \frac{P m}{k T}

Q4PhysicsNEET UG PYQBehaviour of Gases

A container has two chambers of volumes

V_{1} = 2

litres and

V_{2} = 3

litres separated by a partition made of a thermal insulator. The chambers contains

n_{1} = 5

and

n_{2} = 4

moles of ideal gas at pressure

p_{1} = 1

atm and

p_{2} = 2

atm, respectively. When the partition is removed, the mixture attains an equilibrium pressure of:

A1.4 atm

B1.8 atm

C1.3 atm

D1.6 atm

Answer key (D) & worked solution

Correct answer: Option D

v_{1} = 2 L t, v_{2} = 3 L t

n_{1} = 5 m o l, n_{2} = 4 m o l

p_{1} = 1 a t m, p_{2} = 2 a t m

Chamber 1

P_{1} V_{1} = n_{1} R T_{1}

Chamber 2

P_{2} V_{2} = n_{2} R T_{2}

When partition is removed Gasses will mix without loss of energy From kinetic theory of gasses

P V = \frac{2}{3} n (K . E)

For chamber 1

P_{1} V_{2} = \frac{2}{2} n_{1} E_{1}

For Chamber 2

P_{2} V_{2} = \frac{2}{3} n_{2} E_{2}

\frac{3}{2} P_{1} V_{1} = n_{1} E_{1}

\Rightarrow (n_{1} E_{1} + n_{2} E_{2}) = \frac{3}{2} (P_{1} V_{1} + P_{2} V_{2})

\frac{3}{2} P_{2} V_{2} = n_{2} E_{2}

We know

P V = \frac{2}{3} n E

P (V_{1} + V_{2}) = [P_{1} V_{1} + P_{2} V_{2}]

P = \frac{P _{1} V _{1} + P _{1} V _{2}}{V _{1} + V _{2}} = \frac{2 \times 1 + 2 \times 3}{2 + 3}

P = \frac{2 + 6}{5} = \frac{8}{5} = 1.6

Q5PhysicsNEET UG PYQKinetic Theory of an Ideal Gas

One mole of an ideal monatomic gas undergoes a process described by the equation PV

^{3}

= constant. The heat capacity of the gas during this process is

\frac{5}{2} R

B2R

\frac{3}{2} R

Answer key (C) & worked solution

Correct answer: Option C

^{x}

= constant (Polytropic process) Heat capacity in polytropic process is given by

[C = C_{V} + \frac{R}{1 - x}]

Given that PV

^{3}

= constant

\Rightarrow

x = 3 ….. (1) Also, gas is monatomic, so f = 3 ….. (2)

by formula

C = \frac{f R}{2} + \frac{R}{1 - x}

C = \frac{3}{2} R - \frac{R}{2} = R

Q6PhysicsNEET UG PYQBehaviour of Gases

A cylinder contains hydrogen gas at pressure of 249 kPa and temperature 27ºC. Its density is:

(R = 8.3 J m o l^{- 1} K^{- 1})

A0.1

k g / m^{3}

0.02 k g / m^{3}

0.5 k g / m^{3}

0.2 k g / m^{3}

Answer key (D) & worked solution

Correct answer: Option D

From ideal gas equation

∴ P V = n R T

\Rightarrow P V = \frac{m}{M} R T

∴ m = ρ V

P V = \frac{( ρ V ) R T}{M}

ρ = \frac{P M}{R T} \Rightarrow \frac{249 \times 10 ^{3} \times 2 \times 10 ^{- 3}}{8.3 \times 300} \Rightarrow 0.2 k g / m^{3}

Q7PhysicsNEET UG PYQKinetic Theory of an Ideal Gas

The temperature of a gas is

- 5 0^{\circ} C

. To what temperature the gas should be heated so that the rms speed is increased by 3 times?

A3295°C

B3097 K

C223 K

D669°C

Answer key (A) & worked solution

Correct answer: Option A

v_{rms} \propto T

\frac{v _{1}}{v _{2}} = \frac{T _{1}}{T _{2}}

= let initial speed is

v

As speed is increased by 3 times so final speed become

4 v

\Rightarrow \frac{v}{4 v} \frac{223}{T}

T = 3569 K

So temp. in

^{\circ} C = 3568 - 273 = 329 5^{\circ} C

Q8PhysicsNEET UG PYQLaw of Equipartition of Energy and Specific Heat Capacity

An ideal gas is made of polyatomic molecules. Each of the molecules has three translational, three rotational and

f

number of vibrational modes. If the ratio of heat capacities

C_{P} / C_{V}

of the gas is

8/7

, then the value of

f

is:

Answer key (D) & worked solution

Correct answer: Option D

The total internal energy for one mole of gas,

U

= (\frac{3}{2} k_{B} T + \frac{3}{2} k_{B} T + f k_{B} T) N_{A} = (3 + f) k_{B} T N_{A} = (3 + f) R T ∴ C_{V} = \frac{d U}{d T} = (3 + f) R C_{P} = C_{V} + R = (4 + f) R \Rightarrow \frac{C _{P}}{C _{V}} = \frac{4 + f}{3 + f} = \frac{8}{7} (given) \Rightarrow f = 4

Which topics in Kinetic Theory of Gases carry the most questions?

All 5 topics, by tagged PYQs, then practice questions. Counted from the bank. Updated 19 Oct 2026.

Topic	PYQs	Practice questions
Kinetic Theory of an Ideal Gas	12	157
Behaviour of Gases	7	28
Law of Equipartition of Energy and Specific Heat Capacity	5	33
Mean Free Path	3	4
Miscellaneous Examples	0	1

Why does Kinetic Theory of Gases show "–" until you answer 3 questions?

Unknown is not zero. Until you answer at least 3 graded questions in Kinetic Theory of Gases, ViJEEta shows – instead of a zero or a 50% default. Book exercises can raise chapter mastery up to 0.60, adaptive practice up to 0.75, and only a timed chapter test or mock can certify 0.80 and above.

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What happens when you test Kinetic Theory of Gases?

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Chapters either side of Kinetic Theory of Gases by weight

Alternating Current Weight 3.8/100 Gravitation Weight 3.8/100 Work, Energy and Power Weight 3.6/100 Wave Optics Weight 3.4/100

Kinetic Theory of Gases: NEET PYQs and weightage

Kinetic Theory of Gases: formula sheet for NEET

Ideal gas equation

Density form

Kinetic theory pressure

Average KE per molecule

RMS speed

Average and most probable speed

Dalton's law

Equipartition

Change in internal energy

Relation between molar specific heats

Monatomic gas

Diatomic gas (rigid)

Polyatomic gas (f vibrational modes)

Mean free path

How does NEET ask Kinetic Theory of Gases?

Which topics in Kinetic Theory of Gases carry the most questions?

Why does Kinetic Theory of Gases show "–" until you answer 3 questions?

What happens when you test Kinetic Theory of Gases?

Chapters either side of Kinetic Theory of Gases by weight