A compound is made up of iron and oxygen, only. The ratio of iron ions to oxide ions is 2:3 in this Compound . The IUPAC name for this compound is
1. triiron dioxide
2. iron(ll) oxide
3. iron(III) oxide
4. iron trioxide

If the ratio of iron to oxygen is 2:3 then the formula of the compound is Fe203 When we write
correct formulas, we criss-cross the oxidation numbers of the elements and make them into subscripts.
The formula shows that the iron has an oxidation number of +3 in titles compound. The
Roman numeral indicates the oxidation number of the iron: iron (III) oxide.
Therefore the correct answer is 3.