In MnO4-, determine the oxidation state of manganese.

• A. +2
• B. +4
• C. +7
• D. -7

Answer: (C)

Oxidation state is found by assigning typical charges to atoms so that the sum matches the overall charge of the species. In MnO4-, each oxygen is almost always -2, and there are four oxygens, giving -8 total from oxygen. The overall charge is -1, so manganese must provide enough positive charge to bring the sum to -1. Let the oxidation state of manganese be x; x + (-8) = -1, so x = +7. Thus manganese is in the +7 oxidation state in MnO4−. This aligns with permanganate being manganese in its highest common oxidation state. The other options would not balance to the -1 charge.