JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Heat & Thermodynamics

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R

Assertion A: If the average kinetic energy of

H_{2}

and

O_{2}

molecules, kept in two different sized containers are same, then their temperatures will be same.
Reason R: The r.m.s speed of

H_{2}

and

O_{2}

molecules are same at same temperature.
Choose the correct answer from the options given below

Answer: (C)

Solution

The average translational kinetic energy of a molecule is

\frac{3}{2} k T

, set by temperature alone; so if

H_{2}

and

O_{2}

have equal average kinetic energy they must be at the same temperature, and the assertion holds. The r.m.s. speed, however, is

v_{rms} = \frac{3 R T}{M}

, which depends on molar mass; since

H_{2}

(

2 g/mol

) and

O_{2}

(

32 g/mol

) differ in mass, their r.m.s. speeds at the same temperature are not equal, so the reason is false. The assertion is true but the reason is false.

JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Single correct option