How can I find the oxidation number of transition metals?
From the name of the compound containing the transition metal, or by working out the oxidation numbers of all the other atoms in the compound or ion.
Because transition metals have more than one stable oxidation state, we use a number in Roman numerals to indicate the oxidation number e.g. Iron(III) chloride contains iron with an oxidation number of +3, while iron(II) chloride has iron in the +2 oxidation state. The transition metal can be part of the negative ion too, e.g. In potassium chromate(VI) the chromium has an oxidation number of +6.
If you have just a formula, apply the rules for oxidation numbers, e.g. if we had