Which of the following elements of group $15$ $(VA)$ does not show allotropy?

Which of the following compounds does not exist?

How can you synthesise nitric oxide in the laboratory?

The temperature required for electrolysis is maximum for which of the following hydrides?

Nitrous oxide $(N_2O)$:

On heating,compound $(A)$ gives a gas $(B)$ which is a constituent of air. This gas when treated with $3 \, \text{moles}$ of hydrogen $(H_2)$ in the presence of a catalyst gives another gas $(C)$ which is basic in nature. Gas $(C)$ on further oxidation in moist condition gives a compound $(D)$ which is a part of acid rain. Identify compounds $(A)$ to $(D)$ and also give necessary equations of all the steps involved.