The electrolytic decomposition of water gives $H_2$ and $O_2$ in the ratio of

Question

$\begin{array}{1 1} \text{(a) 1 : 2 by volume} \\ \text{ (b) 2 : 1 by volume}\\ \text{ (c) 8 : 1 by mass} \\ \text{ (d) 1 : 2 by mass} \end{array}$