The correct option is D Reducing agent
When moist, SO2 behaves as a reducing agent. It reduces Fe3+ to Fe2+ as
2Fe3+SO2+H2O→2Fe2++4H++SO2−4
A convenient test for the gas is the decolourization of acidified potassium permanganate solution:
5SO2+2MnO−4+2H2O→5SO2−4+4H++2Mn2+
Do note that SO2 here is taken within the context of being a reducing agent in moist conditions. This does not imply that SO2 can only be a reducing agent as can be confirmed by the reaction following reaction:
2H2S+SO2→3S+2H2O
Similarly, SO2 can oxidize active metals like Magnesium to MgO and MgS. With potassium K2S2O3 and K2SO3 are formed.