The root mean square speed of hydrogen gas molecules at 300 K is $1920\mathrm{m}{\mathrm{s}}^{-1}$  . The rms speed of oxygen gas molecules  $\left(\mathrm{in}\mathrm{m}{\mathrm{s}}^{-1}\right)$ at the same temperature is ________

${\mathrm{v}}_{\mathrm{rms}}=\sqrt{\frac{3\mathrm{RT}}{\mathrm{M}}}$
Where R is the gas constant, T is the temperature in kelvin and M is the molecular mass of the gas. 
For the same temperature , ${\mathrm{v}}_{\mathrm{rms}}\propto \frac{1}{\sqrt{\mathrm{M}}}$
$\therefore \frac{\left({\mathrm{v}}_{\mathrm{rms}}\right){\mathrm{H}}_2}{\left({\mathrm{v}}_{\mathrm{rms}}\right){\mathrm{O}}_2}=\sqrt{\frac{{\mathrm{M}}_{{\mathrm{O}}_2}}{{\mathrm{M}}_{{\mathrm{H}}_2}}}\mathrm{or}\frac{\left({\mathrm{v}}_{\mathrm{rms}}\right){\mathrm{H}}_2}{\left({\mathrm{v}}_{\mathrm{rms}}\right){\mathrm{O}}_2}=\sqrt{\frac{32}{2}}=4$
$\mathrm{or}{\left({\mathrm{v}}_{\mathrm{rms}}\right)}_{{\mathrm{O}}_2}=\frac{{\left({\mathrm{v}}_{\mathrm{rms}}\right)}_{{\mathrm{H}}_2}}{4}=\frac{1920}{4}=480{\mathrm{ms}}^{-1}$