Nitrogen forms how many oxides?

Which of the following oxoacids of phosphorus has the strongest reducing property?

Which of the following compounds releases nitrogen dioxide $(NO_2)$ upon heating?

On heating lead $(II)$ nitrate gives a brown gas $'A'$. The gas $'A'$ on cooling changes to a colourless solid $'B'$. Solid $'B'$ on heating with $NO$ changes to a blue solid $'C'$. Identify $'A'$,$'B'$ and $'C'$,write the reactions involved,and draw the structures of $'B'$ and $'C'$.

The oxidation state of phosphorus in cyclo-tri-meta phosphoric acid is

Which one of the following cannot form an amphoteric oxide?