Sodium nitrite is reacted with ${\mathrm{H}}_2{\mathrm{SO}}_4$ to form ${\mathrm{NaHSO}}_4,{\mathrm{HNO}}_3,$ water and $\mathrm{X}$. Gold is dissolved in aqua regia to form water, ${\mathrm{AuCl}}_4^{-}$ and $\mathrm{Y}.\mathrm{X}$ and $\mathrm{Y}$ are respectively

Sodium nitrite reacts with sulphuric acid to form sodium sulphate, nitric acid and nitric oxide.

$2{\mathrm{NaNO}}_2 + {\mathrm{H}}_2{\mathrm{SO}}_4 \to {\mathrm{Na}}_2{\mathrm{SO}}_4 + \mathrm{NO} + {\mathrm{H}}_2\mathrm{O}$

Gold reacts with aqua regia to form nitric oxide, water and a complex of gold.

$\mathrm{Au} + {\mathrm{HNO}}_3 +3\mathrm{HCl} \to {{\mathrm{AuCl}}_4}^{-} + \mathrm{NO} + {\mathrm{H}}_2\mathrm{O}$