Question

What is the name of `H_2SO_3`?

Answer 1

This is `"sulfurous acid"`.

Explanation:

`"Sulfurous acid"` is an hydrate of `"sulfur(IV) oxide"`. It is a much weaker acid than `H_2SO_4`.

In solution it is probably best rationalized as `SO_2*H_2O`, i.e. `"hydrated sulfur dioxide"`. `pK_a=1.81`.