Answer
Fe$_2$O$_5$ is not a compound - no such iron oxide exists. An example of a correct formula is Fe$_2$O$_3$.
Work Step by Step
For iron(III) oxide, we use the +3 ion of iron and the -2 ion of oxygen. Two iron ions and three oxide ions are the lowest whole numbers to have a unit with a balanced charge. Thus, we write Fe$_2$O$_3$.
