The mean translational kinetic energy of one molecule of an ideal gas at temperature $T$ is:

Equipartition theorem: each translational degree of freedom contributes $\dfrac{1}{2} kT$ of energy. There are 3 translational degrees ($x, y, z$), so total mean translational KE per molecule is $\dfrac{3}{2} kT$. For a mole: $\dfrac{3}{2} RT$. If the molecule has internal degrees (rotation, vibration), more energy is stored — but those don't add to **translational** KE specifically.