On repeated sparking 10ml of mixture of carbon monoxide and nitrogen required 7ml of oxygen for combustion of CO and $N_2$ to $CO_2$ and NO.The volume of nitrogen in mixture is (all volumes are measured under identical conditions).

Question

$\begin{array}{1 1}(a)\;\large\frac{7}{2}\normalsize ml&(b)\;4ml\\(c)\;7ml&(d)\;\large\frac{17}{2}\normalsize ml\end{array}$