On the basis of kinetic theory of gases, the mean K.E. of I mole per degree of freedom is

• A

  $\frac{1}{2}\mathrm{RT}$

• B

  $\frac{3}{2}\mathrm{RT}$

• C

  $\frac{1}{2}\mathrm{kT}$

• D

  $\frac{3}{2}\mathrm{kT}$