Find the total number of compounds which produce ${\mathrm{N}}_2$ gas on heating.

$\begin{array}{l}{\mathrm{NH}}_4{\mathrm{NO}}_3,{\mathrm{NH}}_4{\mathrm{NO}}_2,{\mathrm{CH}}_3{\mathrm{COONH}}_4,{\left({\mathrm{NH}}_4\right)}_2{\mathrm{CO}}_3,\\ {\mathrm{NH}}_4{\mathrm{IO}}_3,{\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7,{\left({\mathrm{NH}}_4\right)}_3{\mathrm{PO}}_4\end{array}$

The reactions of the given compounds can be given as,

$\begin{array}{r}{\mathrm{NH}}_4{\mathrm{NO}}_3\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{N}}_2\mathrm{O}+2{\mathrm{H}}_2\mathrm{O}\\ {\mathrm{NH}}_4{\mathrm{NO}}_2\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{N}}_2+2{\mathrm{H}}_2\mathrm{O}\end{array}$

${\mathrm{CH}}_3{\mathrm{COONH}}_4\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{CH}}_3-\stackrel{\underset{\parallel }{\mathrm{O}}}{\mathrm{C}}-{\mathrm{NH}}_2+{\mathrm{H}}_2\mathrm{O}$

$\begin{array}{l}{\left({\mathrm{NH}}_4\right)}_2{\mathrm{CO}}_3\stackrel{\mathrm{\Delta }}{⟶}2{\mathrm{NH}}_3+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2\\ {\mathrm{NH}}_4{\mathrm{IO}}_3\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{N}}_2+{\mathrm{I}}_2+{\mathrm{O}}_2+{\mathrm{H}}_2\mathrm{O}\\ {\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{N}}_2+{\mathrm{Cr}}_2{\mathrm{O}}_3+4{\mathrm{H}}_2\mathrm{O}\\ {\left({\mathrm{NH}}_4\right)}_3{\mathrm{PO}}_4\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{NH}}_3+{\mathrm{P}}_2{\mathrm{O}}_5+{\mathrm{H}}_2\mathrm{O}\end{array}$

Here only 3 compounds produce ${\mathrm{N}}_2$ gas