- In the first reaction, sulfur (S) combines with oxygen (O) to form sulfur dioxide (SO$_2$). In SO$_2$, sulfur has an oxidation state of +2. Since sulfur in its elemental form (S) has an oxidation state of 0, sulfur is oxidized from 0 to +2.
- In the second reaction, sulfur dioxide (SO$_2$) reacts with oxygen to form sulfur trioxide (SO$_3$). In SO$_3$, sulfur has an oxidation state of +6. Therefore, sulfur is further oxidized from +2 to +6.
Thus, sulfur is oxidized from 0 to +2 in the first reaction, and from +2 to +6 in the second reaction.