The correct option is A 52R
As distance between the atoms of a diatomic gas remains constant, vibrational degree of freedom will not be counted.
∴ It possesses only translational and rotational degree of freedom.
⇒f=3(translational)+2(rotational)=5
Since, specific heat at constant volume per gram-mole is molar specific heat at constant volume.
⇒CV=(f2)R
∴CV=52R