For effusion of same volume ,
$\frac{t_1}{t_2} = \sqrt{\frac{M_1}{M_2}}$
This is clearly seen from the options that the
Option (B) is correct
$\frac{^tH_2}{^tO_2} = \sqrt{\frac{M_{H_2}}{M_{O_2}}} = \sqrt{\frac{2}{32}}$
$\frac{^tH_2}{^tO_2} = \frac{1}{4} ; \frac{5}{^tO_2} = \frac{1}{4}$
or $^tO_2 = 5 \times 4 $ = 20 s.
$\frac{5}{\sqrt{2}} = \sqrt{\frac{20}{32}} = \frac{5}{\sqrt{2}}$