Which species is reduced in the reaction 2Br⁻ + Cl₂ → 2Cl⁻ + Br₂?

In the reaction 2Br⁻ + Cl₂ → 2Cl⁻ + Br₂, reduction refers to the gain of electrons by a chemical species. To determine which species is reduced, it's necessary to analyze the changes in oxidation states of the elements involved in the reaction.

Chlorine in its elemental form (Cl₂) starts with an oxidation state of 0. In the product, Cl⁻, chlorine has an oxidation state of -1. Since chlorine has decreased its oxidation state, it has gained electrons during the reaction. This change indicates that chlorine is being reduced.

In contrast, bromide (Br⁻) starts with an oxidation state of -1 in the reactants and ends with Br₂, where bromine has an oxidation state of 0 in the products. This indicates that bromide has lost electrons and is undergoing oxidation, not reduction.

Thus, the species that is undergoing reduction in this reaction is chlorine, as it gains electrons and moves from a higher oxidation state (0) in Cl₂ to a lower oxidation state (-1) in Cl⁻. This process of gaining electrons characterizes reduction.