The number of moles of oxygen obtained by the electrolytic...

($$\begin{array}{ll} 2 \mathrm{H}_2 \mathrm{O} \xrightarrow{\text{ Electrolysis }} 2 \mathrm{H}_2+ &\mathrm{O}_2 \\ 2 \text{mol} & 1 \text{mol} \\ 2 \times 18 =36 g \end{array}$$) (\because 36 \mathrm{~g}) of (\mathrm{H}_2 \mathrm{O}) produce 1 mole of oxygen (\therefore 108 \mathrm{~g}) of water will produce oxygen (=\frac{108}{36}=3 \mathrm{~mol})