Kinetic Theory NEET PYQReal NEET & AIPMT 2006–2020 questions, year-tagged, with solutions
By the RankUp team, founded by Dr. Deepak Sahu (MBBS Gold Medalist, NEET PG AIR 1731) · Updated
Every Kinetic Theory question from the NEET & AIPMT papers on this site (2006–2020), newest first. Each is tagged with its paper. Tap an option to check your answer and read the explanation.
- Chapter
- NCERT Class 11
- PYQs here
- 13
- Papers
- NEET & AIPMT 2006–2020
- In the app
- 491+ questions
Kinetic Theory previous year questions
13 questions. Tap an option to check your answer.
Q1NEET 2020 · Q139
A cylinder contains hydrogen gas at pressure of 249 kPa and temperature 27°C. Its density is : (R = 8.3 J mol⁻¹ K⁻¹)
Not quite — the answer is B.
ρ = PM/RT = (249×10³ × 2×10⁻³)/(8.3 × 300) = 498/2490 = 0.2 kg/m³. Using M = 1 g/mol (atomic H) instead of 2 g/mol for H₂ would give the 0.1 kg/m³ trap.
Q2NEET 2020 · Q155
The mean free path for a gas, with molecular diameter d and number density n can be expressed as :
Not quite — the answer is B.
A molecule sweeps a collision cross-section πd², and allowing for the relative motion of molecules the mean free path is λ = 1/(√2 nπd²). The number density appears only to the first power, and the cross-section must be an area (d²) for λ to have units of length.
Q3NEET 2020 · Q162
The average thermal energy for a mono-atomic gas is : (k_B is Boltzmann constant and T, absolute temperature)
Not quite — the answer is B.
A monatomic molecule has 3 translational degrees of freedom, each carrying ½k_BT by equipartition, so the average energy is (3/2)k_BT. (5/2)k_BT applies to a diatomic molecule with two rotational degrees added.
Q4NEET 2019 · Q12
Increase in temperature of a gas filled in a container would lead to:
Not quite — the answer is B.
Average molecular kinetic energy is proportional to absolute temperature, so heating raises it. In a closed container the mass is fixed and pressure increases (not decreases) with temperature.
Q5NEET 2018 · Q3
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 J K⁻¹)
Not quite — the answer is B.
Set v_rms = √(3k_BT/m) equal to the escape speed 11.2 km/s. T = mv²/(3k_B) = 2.76 × 10⁻²⁶ × (1.12 × 10⁴)² / (3 × 1.38 × 10⁻²³) ≈ 8.36 × 10⁴ K. Using 2k_BT or k_BT instead of 3k_BT gives the other values.
Q6NEET 2017 · Q158
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:
Not quite — the answer is D.
Diatomic O₂ (no vibration) has 5 degrees of freedom: U = 2 × (5/2)RT = 5RT. Monatomic Ar has 3: U = 4 × (3/2)RT = 6RT. Total U = 11RT. Treating O₂ as having 3 degrees of freedom would give 9RT.
Q7NEET 2016 Phase 2 · Q19
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?
Not quite — the answer is B.
PV = NkT gives the number density N/V = P/(kT). Multiplying by the mass of each molecule gives density ρ = Pm/(kT). P/(kT) alone is the number of molecules per unit volume, not mass per unit volume.
Q8NEET 2016 Phase 1 · Q25
The molecules of a given mass of a gas have r.m.s. velocity of 200 ms⁻¹ at 27°C and 1.0 × 10⁵ Nm⁻² pressure. When the temperature and pressure of the gas are respectively, 127°C and 0.05 × 10⁵ Nm⁻², the r.m.s. velocity of its molecules in ms⁻¹ is:
Not quite — the answer is B.
v_rms = √(3RT/M) depends only on temperature, not pressure. v₂ = 200 × √(400/300) = 200 × 2/√3 = 400/√3 m/s. Scaling with pressure is the trap that leads to the smaller values.
Q9AIPMT 2015
The ratio of the specific heats Cp/Cv = γ in terms of degrees of freedom (n) is given by:
Not quite — the answer is D.
With n degrees of freedom C_v = (n/2)R and C_p = (n/2 + 1)R, so γ = C_p/C_v = 1 + 2/n. For a monatomic gas (n = 3) this gives 5/3 as expected.
Q10AIPMT 2014
The mean free path of molecules of a gas, (radius 'r') is inversely proportional to:
Not quite — the answer is A.
λ = 1/(√2 π d² n) with molecular diameter d = 2r, so the mean free path is inversely proportional to r².
Q11NEET 2013
The molar specific heats of an ideal gas at constant pressure and volume are denoted by Cp and Cv, respectively. If γ = Cp/Cv and R is the universal gas constant, then Cv is equal to
Not quite — the answer is B.
Mayer's relation Cp − Cv = R with Cp = γCv gives γCv − Cv = R, so Cv = R/(γ − 1). The expression γR/(γ − 1) would be Cp, and (γ − 1)/R is the inverse of the correct result.
Q12AIPMT 2008 Prelims · Q16
At 10°C the value of the density of a fixed mass of an ideal gas divided by its pressure is x. At 110°C this ratio is
Not quite — the answer is A.
From PV = (m/M)RT, ρ/P = M/(RT), so the ratio is inversely proportional to absolute temperature. At 383 K it becomes x × 283/383. Using Celsius temperatures (10/110) is wrong because gas laws need kelvin.
Q13AIPMT 2006 Prelims · Q33
The molar specific heat at constant pressure of an ideal gas is (7/2)R. The ratio of specific heat at constant pressure to that at constant volume is :
Not quite — the answer is A.
For an ideal gas Cv = Cp − R = (7/2)R − R = (5/2)R. Hence γ = Cp/Cv = (7/2)/(5/2) = 7/5, as for a diatomic gas. A ratio below 1 is impossible because Cp is always larger than Cv.
How often Kinetic Theory came up
Questions from this chapter in each paper on this site.
Keep going
PYQs show what NEET asks. For the full Kinetic Theory bank (491+ questions with solutions), use the RankUp app.
