FeO is Iron II Oxide. You identify that it's an ionic bond so it won't have any prefixes. By reverse criss-crossing the charges, Iron gets a 1+ charge, and Oxygen gets a 1- charge. Since you know that Oxygen has to have a 2- charge, you multiply the 1+ and 1- by 2 to fix their charges, thus giving Iron a 2+ charge and Oxygen a 2- charge.
Since Iron has a 2+ charge, it's roman numeral is II. So the answer is Iron II Oxide.
The other one is Iron III Oxide. By reverse criss-crossing the charges, Fe geta 3+ charge, and Oxygen gets a 2- charge. Since it's correct, the 3+ charge is the roman numeral. So, the answer is Iron III Oxide.
