At the same temperature the ratio between RMS velocity of H₂ and RMS velocity of O₂ is

The rms velocity is directly proportional to the square root of temperature and inversely proportional to the square root of molecular weight.

$$\begin{gathered} \frac{{\mathrm{V}}_{{\mathrm{H}}_2}}{{\mathrm{V}}_{{\mathrm{O}}_2}}=\sqrt{\frac{{\mathrm{M}}_{{\mathrm{O}}_2}}{{\mathrm{M}}_{{\mathrm{H}}_2}}} \\ \frac{{\mathrm{V}}_{{\mathrm{H}}_2}}{{\mathrm{V}}_{{\mathrm{O}}_2}}=\sqrt{\frac{32}{2}} \\ \frac{{\mathrm{V}}_{{\mathrm{H}}_2}}{{\mathrm{V}}_{{\mathrm{O}}_2}}=\sqrt{\frac{16}{1}} \\ {\mathrm{V}}_{{\mathrm{H}}_2}:{\mathrm{V}}_{{\mathrm{O}}_2}=4:1 \end{gathered}$$