According to law of equi-partition of energy the molar specific...

For a rigid diatomic gas, the number of translational degrees of freedom is $3$ and the number of rotational degrees of freedom is $2$.

Total degrees of freedom, $f = 3 + 2 = 5$.

According to the law of equipartition of energy, the molar specific heat at constant volume is given by:

$C_v = \dfrac{f}{2} R = \dfrac{5}{2} R$

Using Mayer's relation, the molar specific heat at constant pressure is:

$C_p = C_v + R$

$C_p = \dfrac{5}{2} R + R = \dfrac{7}{2} R$

Answer: $\dfrac{7R}{2}$