Question

What is the formula for iron (IV) oxide?

Answer 1

`FeO_2`

Explanation:

O has a charge of -2 and since you're told Fe has a charge of +4 based of the roman numeral, you need 2 Oxide ions to balance out the charge on Fe.

Answer 2

It's `Fe_2O_4` or `FeO_2`

Explanation:

Valence of iron=4
Valence of oxygen=2
When you find the least common multiple it's 8, and you divide it with valences of the particular elements.
But you can also divide the equation with 2 to get `FeO_2`