Which of the following oxides of nitrogen is a mixed anhydride of two acids?

Which of the following elements forms $p\pi-p\pi$ bond with itself?

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 $((HPO_{3})_{n})$

Identify the compound in which phosphorus exists in the oxidation state of $+1$.

With which of the following does $FeSO_4$ form a brown ring?

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