What is the oxidation number of iron oxide?

As a transition metal , iron exhibits several oxidation numbers.

As FeO (Ferrous Oxide) its oxidation no,. is ;2; usuallu written as 'Iron(II)Oxide'. This is pale green in colour

As F2O3(Ferric Oxide) its oxidation No. is '3' usually written as Iron(III)Oxide. This in (Rust) Brown/Red in colour. Gives human blood its red colour.

NB Note the Roman Numerals to indicate oxidation state.

NNB Iron has six(6) electrons in its outer(valence) 'd' electron shell. The oxidation numbers indicates that only '2' or '3' as the case may be, electrons are involved in combining with another atom. The other electrons remain uncombined.