Q.

The standard heat of formation of ${\text{NO}}_{\text{2}}\left(\text{g}\right)$ and ${\text{N}}_{\text{2}}{\text{O}}_{\text{4}}\left(\text{g}\right)$ are 8.0 and $\text{4}{\text{.0 kcal mol}}^{\text{–1}}$ respectively. The heat of dimerisation of ${\text{NO}}_{\text{2}}$ in kcal is