What do ${\mathrm{HNO}}_2$decomposes into?

1. ${\mathrm{HNO}}_2$ is Nitrous acid, which is a weak monoprotic acid.
2. Nitrous acid$\left({\mathrm{HNO}}_2\right)$ is found in the gaseous phase and is generally used in making diazonium salts from amines.
3. Acidification of Sodium nitrite with a mineral acid in an aqueous solution produces Nitrous acid.
4. The decomposition of Nitrous acid in the gaseous phase may produce Nitrogen dioxide$\left({\mathrm{NO}}_2\right)$, Nitric oxide$\left(\mathrm{NO}\right)$, and water$\left(H_{2}O\right)$.
5. The chemical reaction is represented as follows:
   $\underset{(\mathrm{Nitrous}\mathrm{acid})}{2{\mathrm{HNO}}_2\left(\mathrm{g}\right)}\to \underset{(\mathrm{Nitrogen}\mathrm{dioxide})}{{\mathrm{NO}}_2\left(\mathrm{g}\right)}+\underset{(\mathrm{Nitric}\mathrm{oxide})}{\mathrm{NO}\left(\mathrm{g}\right)}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$