# A 40 mL of a mixture of $H_2O$ and $O_2$ was placed in a gas burette at $18^{\large\circ}C$ and 1 atm P. A spark was applied so that the form a pure gas had a volume of 10mL at $18^{\large\circ}C$ and 1 atm P . If the remaining gas was $H_2$, what was the initial mole $\%$ of $H_2$ in mixture?
$(a)\;76\%\qquad(b)\;75\%\qquad(c)\;74\%\qquad(d)\;78\%$