Question

What is the oxidation number of manganese (Mn) in potassium permanganate (KMnO4)?

+3

+5

+6

+7

Answer 1

To find the oxidation # of a piece of a molecule, there are really only a few things to remember:
1) the total charge of the molecule must equal zero.
2) the common monatomic ions have their normal charges (K is a +1, Ca would be a +2, etc)
3) oxygen is always a -2 (except in a peroxide like H2O2, where it's -1 each).

Assemble the molecule so that

\[K + Mn + 4*O = 0\]\[(+1) + (?) + 4(-2) = 0\]
the only # that fits is +7