A non-metal $A$, which is the largest constituent of air, when heated with $H_2$ in a $1 : 3$ ratio in the presence of a catalyst $(Fe)$, gives a gas $B$. On heating with $O_2$, it gives an oxide $C$. If this oxide is passed into water in the presence of air, it gives an acid $D$, which acts as a strong oxidising agent.
$(a)$ Identify $A$, $B$, $C$, and $D$.
$(b)$ To which group of the periodic table does this non-metal belong?

$(A) A = N_2$ (Nitrogen), $B = NH_3$ (Ammonia), $C = NO$ (Nitric oxide), $D = HNO_3$ (Nitric acid).
Step $1$: Nitrogen $(N_2)$ is the most abundant gas in the atmosphere.
Step $2$: Haber's process: $N_2 + 3H_2 \xrightarrow{Fe} 2NH_3$ (Gas $B$).
Step $3$: Catalytic oxidation: $N_2 + O_2 \rightarrow 2NO$ (Oxide $C$).
Step $4$: Formation of acid: $4NO + 3O_2 + 2H_2O \rightarrow 4HNO_3$ (Acid $D$).
$(b)$ Nitrogen $(N_2)$ belongs to Group $15$ of the Periodic Table.