Question

Assertion The molecules of a monatomic gas has three degree of freedom.
Reason The molecules of a diatomic gas has five degree of freedom.

• A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
• B. If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion
• C. If Assertion is true but Reason is false
• D. If both Assertion and Reason are false

Answer 1

Answer: (B)

A monoatomic gas molecules (like the consists of a single atom. It can have translational motion in any direction in space. Thus, it has $3$ translational degrees of freedom $f=3$ (all translational)
It can also rotate but due to its small moment of inertia rotational kinetic energy is neglected. The molecules of a diatomic gas (like $O _{2}, CO _{2}, H _{2}$ ) cannot only move bodily but also rotate about any one of the three coordinate axes.
Hence it can have only two rotational degrees of freedom.
Thus, a diatomic molecule has $5$ degree of freedom $3$ translational and $2$ rotational.