Question

Assertion : The molecules of a monoatomic gas has three degrees of freedom.
Reason : The molecules of a diatomic gas has five degrees of freedom.

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

Answer 1

Answer: (B)

A monoatomic gas molecule (like $He$) 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 $O_2,C{O}_2,H_2$ ) cannot only move bodily but also rotate about any one of the three coordinate axes. Hence, it can have two rotational degrees of freedom.
Thus, a diatomic molecule has $5$ degrees of freedom: $3$ translational and $2$ rotational.