State a reaction in which SO₂ acts as an oxidizing agent.

Oxidizing agent:

The oxidizing agents are the elements that reduce themselves and oxidize other elements present in the reaction.

Sulphur dioxide as an oxidizing agent:

The sulphur dioxide acts as both reducing and oxidizing agents due to its multiple valencies. The oxidation state of the sulphur varies between -2, 0, +2, +4, and +6.

When sulphur dioxide is reacting with hydrogen sulphide, it oxidizes(addition of oxygen) hydrogen sulphide and itself get reduced to elemental sulphur.

$$\begin{gathered} {\mathrm{SO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+3\mathrm{S}\left(\mathrm{s}\right) \\ +40 \end{gathered}$$

Here, sulphur has a +4 oxidation state that is reducing to 0 in elemental sulphur and it is oxidizing the other substance.