The ratio of the average molecular kinetic energy of ${\mathrm{UF}}_6$ to that of ${\mathrm{H}}_2$ both at 300 K is :

Average kinetic energy is only a function of temperature, per the Kinetic Molecular Theory of Gases. The following is the formula for average molecule kinetic energy:

$K.E.=\frac{3}{2}k\times T$

K is the botlzmann constant

T is temperature