##Fe_2O_3##
You have to balance the atoms first with their charges. Iron or Fe is a transition metal. Transition metals as a whole group do not have a specific charge. Iron has different charges but in this case, it’s charge is +3.
Oxygen has a charge of -2 since it is in column 16, shown in the table.
Now you must balance the atomic charges. To do that, you want the charges of the iron and the oxygen to cancel.
So, for iron, you multiply its charge of +3 by 2 to get +6 You are taking 2 atoms of iron(III) (or iron atoms with a charge of +3) so it is written as ##Fe_2##.
For oxygen, you multiply -2 by 3 to get -6. You have 3 oxygen atoms with a charge of -2, so the answer is ##Fe_2O_3##.
Check your work by adding up the charges.
-6+6=0, which works since you get a net charge of 0.
Check this video out!
NOTE
– When I say charge, each element has a certain number of (electrons in their outer shell). So, if you are in Group 1 (the alkali metals), you would have a +1 charge.
– Your charge is based on columns or families (horizontal!). This is shown in the picture