N2( g)+21O2→N2O(g) 
$\begin{aligned}
\Delta \mathrm{H}{\mathrm{f}}{ }^{\mathrm{o}}= & {[\text { Energy required for breaking of bonds }] } \
& -[\text { Energy released for forming of bonds }] \
= & \left(\Delta \mathrm{H}{\mathrm{N} \equiv \mathrm{N}}+\frac{1}{2} \Delta \mathrm{H}{\mathrm{O}=\mathrm{O}}-\left(\Delta \mathrm{H}{\mathrm{N}=\mathrm{N}}+\Delta \mathrm{H}_{\mathrm{N}=\mathrm{O}}\right)\right. \
= & \left(946+\frac{1}{2} \times 498\right)-(418+607)=170 \mathrm{kJ} \mathrm{mol}^{-1} \
& \text { Resonance energy }=170-82=88 \mathrm{kJ} \mathrm{mol}^{-1}
\end{aligned}$