Physics - Heat & Thermo Question with Solution | TestHub

Both ${\mathrm{H}}_2$ and He have the same degrees of translational freedom (3), so average translational $\mathrm{KE}=\frac{3}{2}kT$ is the same. But ${\mathrm{H}}_2$ has more total degrees of freedom (5 vs 3), so its molecules have greater average energy. Speed $\propto 1/\sqrt{M}$, so speeds differ.