If, in the reaction $N_2O_4 \equiv 2NO_2$, x is that part of $N_2O_4$ which dissociates, then the number of molecules at equilibrium will be

Question

$\begin{array}{1 1} (a)\;1 \\ (b)\;3 \\ (c) \;(1+x) \\ (d)\;(1+xy)^2 \end{array}$