On heating lead $(II)$ nitrate gives a brown gas $'A'$. The gas $'A'$ on cooling changes to a colourless solid $'B'$. Solid $'B'$ on heating with $NO$ changes to a blue solid $'C'$. Identify $'A'$,$'B'$ and $'C'$,write the reactions involved,and draw the structures of $'B'$ and $'C'$.

(N/A) $2 \ Pb(NO_3)_2 \xrightarrow{\Delta, 673 \ K} 2 \ PbO + 4 \ NO_2 + O_2$
Gas $'A'$ is $NO_2$ (Brown gas).
Upon cooling,$2 \ NO_2 \rightleftharpoons N_2O_4$. Thus,solid $'B'$ is $N_2O_4$.
$N_2O_4 + NO \xrightarrow{250 \ K} N_2O_3$
Solid $'C'$ is $N_2O_3$ (Blue solid).
Structures:
$N_2O_4$: The structure consists of two $NO_2$ units linked by an $N-N$ bond,showing resonance.
$N_2O_3$: The structure consists of $NO_2$ and $NO$ units linked by an $N-N$ bond,showing resonance.