SOLUTION —
Let the number of moles of each gas $=x$
Fraction of hydrogen escaped $=\frac{1}{2} x$
$\begin{array}{l}\Rightarrow \frac{n_{\mathrm{O}_2} / t}{\frac{x}{2} / t}=\frac{1}{4} \Rightarrow n_{\mathrm{O}_2}=\frac{1}{8} x \\\end{array}$
Hence, fraction of oxygen escaped $=\frac{1}{8}$
So, The correct option of this question will be (C).