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Physics Question 33 – JEE-MAIN 2026

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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 H2 and O2 molecules, kept in two different sized containers are same, then their temperatures will be same. Reason R: The r.m.s. speed of H2 and O2 molecules are same at same temperature. Choose the correct answer from the options given below

Recall the fundamental relationships between temperature, average kinetic energy, and molecular speed for ideal gases.

Step 1: Analyze Assertion A✦ Active

The average kinetic energy of gas molecules is given by the formula Eavg=32kT, where k is the Boltzmann constant and T is the absolute temperature. This formula shows that the average kinetic energy depends only on the absolute temperature and is independent of the type of gas molecule (mass) or the volume of the container. Therefore, if the average kinetic energy of H2 and O2 molecules is the same, their temperatures must be the same. Assertion A is true.

Step 2: Analyze Reason R○ Expand

The root mean square (r.m.s.) speed of gas molecules is given by vrms=3RTM, where R is the ideal gas constant, T is the absolute temperature, and M is the molar mass of the gas. For H2, MH2=2 g/mol, and for O2, MO2=32 g/mol. Since MH2≠MO2, their r.m.s. speeds will not be the same at the same temperature. Specifically, vrms,H2>vrms,O2 at the same temperature. Therefore, Reason R is false.

Step 3: Conclusion○ Expand

Based on the analysis, Assertion A is true and Reason R is false. This corresponds to option 3.

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