In the permanganate ion MnO4-, the oxidation number of each oxygen atom is - 2. What is the oxidation number of the manganese ion?

A. + 1

B. + 2

C. + 7

D. + 8

To determine this simply multiply the number of oxygen atoms by the oxidation number for each oxygen atom, which is 4 • - 2 = - 8. Then knowing we have 1 Mn atom, it would be 1 • x, where x is the unknown oxidation state for Mn.

X + - 8 = overall charge of compound

X + - 8 = - 1

X - 8 = - 1

X = 7.

The solution is C.