Answer
The formula of chlorous acid is $HClO_{2}$.
Work Step by Step
Oxyacids with oxanions ending in -ite are named as : $ 'base name \hspace{1mm}of \hspace{1mm}oxyanion' + ous + acid$
Here, $chlor$ is the basename and the oxyanion ends in $-ite$. so, the oxyanion is chlorite: $ClO_{2}^{-}$. To balance the charges,1 hydrogen ion is present. So, the formula of chlorous acid is $HClO_{2}$.