When nitric oxide reacts with nitrogen dioxide there is formation of dinitrogen trioxide (N2O3), which is blue coloured in liquid and solid state. Chemical reaction is as follows
NO
Nitric‌o‌x‌i‌d‌e
+
NO2
Nitrogen‌dioxide
250K
────▶
‌‌
N2O3
Dinitrogen‌trioxide(P)(Blue)
(b) Dinitrogen tetraoxide is in equilibrium with nitrogen dioxide which is colourless compound.
N2O4
Nitrogen‌dioxide
⇌
2NO2
Dinitrogen‌tetra‌oxide(Q)(colourless)
(c) It is a decomposition reaction which means a single type of chemical compound breaks down into two or more. NO2 formed is brown colour gas.
2Pb(NO3)2
Lead‌nitrate
673K
────▶
2PbO
Lead‌oxide
+
4NO2
Nitrogen‌dioxide
+
O2
Oxygen
(d) Nitric acid reacts with P4O10 to give phosphorus acid and dinitrogen pentaoxide which is colourless.