HBr + H₂SO₄ SO₂ + Br₂ + H₂O

What is the oxidation number of the oxidizing agent?

What is the oxidation number of the reducing agent?

The reaction equation is:

HBr + H₂SO₄ → SO₂ + Br₂ + H₂O

An oxidizing agent is a substance that itself becomes reduced and oxidizes the other chemical species in the reaction mixture. A reducing agent is similar, except that it becomes oxidized and reduces the other substance.

In the reaction, the valency of bromine changes from - 1 to 0, so it is oxidized, making it the reducing agent. The valency of sulfur changes from + 6 to + 4, so it is reduced, making it the oxidizing agent.