Q:

Why does bisulfite (HSO3-) act as a base in this reaction?

I don't understand why the answer is (A) since $\ce{HSO_3^-}$ gives its proton out and becomes $\ce{SO_2}$ or $\ce{(SO_3)^{2-}}$ as show in both equations above, it'd rather be an acid. There is also no change in oxidation numbers of any of these atoms, too.

A:

I think HSO3 acts as a base because it donates a pair of electrons and this is another definition when you think of acids and bases. An acid is a substance that accepts a pair of electrons whereas a base is a substance that donates a pair of electrons.

