Two oxides of nitrogen,$NO$ and $NO_2$ are allowed to react together at $243 \ K$ to form a coloured compound of nitrogen $(X)$. When compound $(X)$ reacts with water,it yields another compound of nitrogen $(Y)$. The shape of the anion of $(Y)$ molecule is:

Superphosphate is the mixture of

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.

$H_3PO_2$ $\xrightarrow{140^{\circ}C}$ $A$ $\xrightarrow{250^{\circ}C}$ $B$ $\xrightarrow{316^{\circ}C}$ $C$
Compound $(C)$ is

What happens when iron is treated with concentrated nitric acid $(HNO_3)$?

State the oxoacids of phosphorus with their formula,methods of preparation,and the presence of characteristic bonds in their structure.