What is the oxidation-state change of manganese in MnO4− when it is reduced to Mn2+?

• A. From 0 to +2, gain of 2 electrons.
• B. From +7 to +4, loss of 3 electrons.
• C. From +7 to +2, a loss of 5 electrons.
• D. From +2 to +7, gain of 5 electrons.

Answer: (C)

The key idea is tracking oxidation states and electron transfer during a reduction. In MnO4−, manganese has an oxidation state of +7 (oxygen contributes -2 each, so 4×(-2) = -8; +7 + (-8) = -1 overall). In Mn2+, manganese is +2. Reducing manganese means it must gain electrons, so going from +7 to +2 involves gaining 5 electrons. So the correct description is that manganese changes from +7 to +2 with a gain of 5 electrons. Some wording that says “loss of 5 electrons” would contradict the fact that reduction adds electrons.