Which statements are correct about degrees of freedom? A. A...

According to the equipartition of energy, each degree of freedom carries $\dfrac{1}{2}RT$ energy per mole and total energy per mole of a gas having $n$ degrees of freedom is $\dfrac{1}{2}nRT$. Therefore, statement A is wrong and statement B is correct.

A monoatomic molecule only has translational degrees of freedom and does not have rotational degree of freedom. For a polyatomic model there are three rotational degrees of freedom and three translational degrees of freedom. Therefore, statement C is incorrect and statement D is correct.