Consider the reaction. 2 cap k plus Br sub 2 rightarrow 2 cap k raised to the plus 2 power Br raised to the negative power What is being reduced?

Reduction is a gain of electrons, which lowers an element’s oxidation number. In Br₂, bromine has an oxidation number of 0; in KBr, bromine is −1, so Br₂ gains electrons and is reduced. Potassium changes from 0 to +1, so potassium is oxidized, not reduced. The correct choice is only Br₂.

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