# What is the name of H_2SO_3?

This is $\text{sulfurous acid}$.
$\text{Sulfurous acid}$ is an hydrate of $\text{sulfur(IV) oxide}$. It is a much weaker acid than ${H}_{2} S {O}_{4}$.
In solution it is probably best rationalized as $S {O}_{2} \cdot {H}_{2} O$, i.e. $\text{hydrated sulfur dioxide}$. $p {K}_{a} = 1.81$.