# 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

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

$2NO_2(g) \rightarrow N_2O_4$
$(N_2O_4) - 2 \Delta H_f\: \Delta H = \Delta H_f\: (NO_2) = 2 – 2(8) = -14 \: kJ/mol$
Abs : (C)