The standard enthalpies of formation of $NO_2(g)\: and\: N_2O_4(g)$ are $8$ and $2\: kcal/mol$ respectively. The heat of dimerisation of $NO_2$ in gaseous state is

Question

$\begin {array} {1 1} (A)\; 10\: kcal/mol & \quad (B)\; 6\: kcal/mol \\ (C)\;-14\: kcal/mol & \quad (D)\;-6 \: kcal/mol \end {array}$