a
$\mathop {{C_x}{H_y}}\limits_{\left( {\frac{{25}}{M}} \right)} + \left( {x + \frac{y}{4}} \right){O_2} \to \mathop {\mathop {xC{O_2}}\limits_{x \times \frac{{25}}{M}} }\limits_{ = 2} + \mathop {\mathop {\frac{y}{2}{H_2}O}\limits_{\frac{y}{2} \times \frac{{25}}{M}} }\limits_{ = 0.5} $
$C\,\,\,\,\,\,\,\,\,\,\,x \times \frac{{25}}{M} = 2$
$H\,\,\,\,\,\,\,\,\,\,\,y \times \frac{{25}}{M} = 1$
$C_{2y}H_y \equiv 24\,y\,gm\,C + y\,gm\,H$
or
$24 : 1$ ratio by mass