Nitric oxide $(NO)$ is prepared by the action of dilute $HNO_3$ on which of the following metals?

$Sn$ is dissolved in excess of $NaOH$ solution,the compound obtained is

Nitric acid oxidises phosphorus to

Which of the following, when subjected to thermal decomposition, will liberate dinitrogen?
$(i)$ Sodium nitrate
$(ii)$ Ammonium dichromate
$(iii)$ Barium azide

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

$NaH_2PO_4$ $\xrightarrow{230^\circ C}$ $Na_3P_3O_9$ $\xrightarrow{638^\circ C}$ $(NaPO_3)_n$ $\rightarrow D$ (glossy solid).
Compound $D$ is sodium hexametaphosphate,which is known as: