In the compound fe203 irons oxidization number is + 3 + Oxygen's oxidation number is

-2

Explanation:

Since its a compound, it's charge is 0.

So, there are 2 Fe and 3 Oxygen,

let x = oxidation number of oxygen

2 (+3) + 3x = 0

x = -2

Side note : even if the oxidation number is positive, make sure to put the positive sign like how you would in numbers