On heating, lead $\left(\mathrm{II}\right)$ nitrate gives a brown gas $\left(\mathrm{A}\right)$. The $\left(\mathrm{A}\right)$ on cooling changes to a colourless solid/liquid $\left(\mathrm{B}\right)$.on heating with $\mathrm{NO}$ changes to a blue solid $\left(\mathrm{C}\right)$. oxidation number of nitrogen in solid $\left(\mathrm{C}\right)$ is