In the redox reaction, use oxidation numbers to identify the oxidized, the reduced, the oxidizing agent and the reducing agent.?

Br⁻ + 6IO₃⁻+ 6H⁺ → 5BrO₃⁻ + 3I₂ + 3H₂O

Br⁻ is oxidized because the oxidation number of Br increases from -1 (in Br⁻) to +5 (in BrO₃⁻).
Hence, Br⁻ acts as the reducing agent.

IO₃⁻ is reduced because the oxidation number of I decreases from +5 (in IO₃⁻) to -1 (in I⁻).
Hence, IO₃⁻ acts as the oxidizing agent.