# How can I find the oxidation number of transition metals?

If you have just a formula, apply the rules for oxidation numbers, e.g. if we had $K M n {O}_{4}$ then we know that K always has an oxidation number of +1 in its compounds, and O is always -2 except in peroxides, so here we have +1 and 4 x -2 so the oxidation number of the Mn must be +7 because the oxidation numbers in a compound sum to zero.