Velocity of sound in a gascous medium is

$\quad v=\sqrt{\frac{\gamma R T}{M}}$

$\Rightarrow \quad v \propto \frac{1}{\sqrt{M}}$

$\text { So, } \quad \frac{v_{\text {Oxygen }}}{v_{\text {Hydrogen }}}=\sqrt{\frac{M_{ H }}{M_0}}=\sqrt{\frac{2}{32}}$

$\Rightarrow \quad \frac{v_{\text {Oxygen }}}{v_{\text {Hydrogen }}}=\frac{1}{4}$