The element which catches fire in air at $30^o\,C$ and is stored under water is

Which of the following oxides is the anhydride of orthophosphoric acid?

The oxide without a nitrogen-nitrogen bond is:

Draw the structures of different oxoacids of phosphorus and indicate the oxidation state of phosphorus,characteristic bonds,and their numbers in each.

The molecular formula of metaphosphoric acid is

$A + H_2O \to B + HCl$ and $B + 3H_2O \to C + 3HCl$. Compounds $(A)$,$(B)$,and $(C)$ are respectively: