ANSWER
[tex]SO_4^{2-}(aq)\text{ --------- option C}[/tex]STEP-BY-STEP EXPLANATION:
Sulfite ion is readily oxidized to sulfate. This occurs because sulfite ion is exposed to air for a long period of time. Oxidation occurs with atmospheric oxygen.
Below is the oxidation reaction of sulfite ion
[tex]2SO_3^{2-}(aq)\text{ + }O_{2(g)\text{ }}\rightarrow2SO_4^{2-}(aq)[/tex]Hence, the possible oxidation product is option C