A tautomeric constitution for nitrous acid : \(\begin{matrix} H & & \\ \mid & & \\ O & -N = O \end{matrix}\) \(\begin{matrix} acids & & \\ \rightleftharpoons& & \\ bases & \end{matrix}\) \(\begin{matrix} H & & \\ \mid & & \\ O =N = O \end{matrix}\) explains many otherwise obscure observations. The \(hydroxy\) form predominates. Mineral acids favour the \(nitro\) form and the- change proceeds rapidly; the reverse change is slow. It is the \(nitro\) form which acts as an oxidising agent.