Which one of the following reducing agents can also act as an oxidizing agent ?

Sulfur dioxide (SO2) can act as both a reducing agent and an oxidizing agent due to the intermediate oxidation state of sulfur (+4). In SO2, sulfur can be oxidized to a +6 state (as in sulfate ions or SO3), making it a reducing agent [t2]. Conversely, it can be reduced to a 0 state (elemental sulfur) or -2 state (H2S), allowing it to act as an oxidizing agent [t2][t8]. In contrast, H2S and HI typically act only as reducing agents because sulfur and iodine are in their lowest common oxidation states (-2 and -1 respectively), meaning they can only be oxidized [t1]. While H2 can act as an oxidizing agent when reacting with active metals to form ionic hydrides [c5], SO2 is the classic example of a substance exhibiting dual redox behavior in standard chemical contexts [t1][t8].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > What you have learnt > p. 56