If the R.M.S. speed of oxygen molecules at 0 ° C is 160m s ^ - 1 ....

Recall the formula of root mean square speed, ${v}_{RMS} = \sqrt{\dfrac{3RT}{M}}$,

$⇒ \dfrac{{\left({v}_{RMS}\right)}_{{O}_{2}}}{{\left({v}_{RMS}\right)}_{{H}_{2}}} = \sqrt{\dfrac{{M}_{{H}_{2}}}{{M}_{{O}_{2}}}} = \sqrt{\dfrac{2}{32}} = \dfrac{1}{4}$

$⇒ {\left({v}_{RMS}\right)}_{{H}_{2}} = 4{\left({v}_{RMS}\right)}_{{O}_{2}} = 4 \times 160 = 640{\text{m s}}^{- 1}$