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

[![enter image description here](https://i.stack.imgur.com/gwfNP.png)](https://i.stack.imgur.com/gwfNP.png)


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.




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.


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