In the compound Fe2O3, iron's oxidation number is +3, and oxygen's oxidation number is
Answer here

The oxygen's oxidation number is -2.

Explanation:

For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.

In , Fe is having an oxidation state of +3 called as  cation and oxygen  is an anion with oxidation state of -2. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral

The cations and anions being oppositely charged attract each other through strong coloumbic forces and form an ionic bond.

-2 just took the test on

you need to have a picture of the atom that way we can answer it