Two oxides of nitrogen,$NO$ and $NO_2$,react together at $253 \ K$ to form a compound of nitrogen $X$. $X$ reacts with water to yield another compound of nitrogen $Y$. The shape of the anion of $Y$ is:

Which of the following orders is correct?

The number of $H$ atoms attached to the phosphorus atom in hypophosphorous acid is

Phosphorus reacts with chlorine gas to give a colourless liquid,which fumes in moist air to produce $HCl$ and

The element that does $NOT$ exhibit allotropy is$-$

Draw the structures of the following oxoacids of phosphorus:
$(i)$ Orthophosphoric acid $(H_{3}PO_{4})$
$(ii)$ Pyrophosphoric acid $(H_{4}P_{2}O_{7})$
$(iii)$ Orthophosphorus acid $(H_{3}PO_{3})$
$(iv)$ Hypophosphorus acid $(H_{3}PO_{2})$
$(v)$ Cyclotrimetaphosphoric acid $((HPO_{3})_{3})$
$(vi)$ Polymetaphosphoric acid $((HPO_{3})_{n})$