$(i)\, {\Delta _f}{H^o}$ of $N_2O$ is $82\, kJ\, mol^{-1}$
$(ii)$ Bond energies of $N \equiv N,N = N,O = O$ and $N = O$ are $946, 418, 498$ and $607\, kJ\, mol^{- 1}$ respectively
The resonance energy of $N_2O$ is......$kJ$
$N\equiv N(g)+\frac{1}{2}(O=O\to )\overset{-}{\mathop{\underset{\centerdot \,\centerdot }{\overset{\centerdot \,\centerdot }{\mathop{N}}}\,}}\,=\overset{+}{\mathop{N}}\,=\underset{\centerdot \,\centerdot }{\overset{\centerdot \,\centerdot }{\mathop{O}}}\,(g)$
$\Delta H_f^o = $ [Energy required for breaking of bonds] - [Energy released for forming of bonds]
$=(\Delta {{H}_{N=N}}+\frac{1}{2}\Delta {{H}_{O=O}}-(\Delta {{H}_{N=N}}+\Delta {{H}_{N=O}})$
$ = (946 + \frac{1}{2} \times 468) - (418 + 607) = 170\,kJ\,mo{l^{ - 1}}$
Resonance energy $ = 170 - 82 = 88\,kJ\,mo{l^{ - 1}}$
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