The option B is correct option.
The half-reaction 2MnO2 + H2O + 2e- Mn2O3 is missing OH- ions.
Full equation:
2MnO2 + H2O + 2e- → Mn2O3 + 2OH-
The oxidation number of S in SO2−4 is 0.
Because in ionic compounds sum of oxidation number is equal to charge.
If compound is SO4-2 then option d will correct option.
Because (+6) + (-2 * 4) = -2