X would be the metal in Ionic Formulas. These equations you will be solving for X and X alone every time.
5
the answer is Pie
Ionic x
Al3+ N3-
formula units
2 FeO
BaI2 is ionic. Rest are covalent compounds.
Ionic compounds are conventionally represented by chemical formulas; but after contemporary knowledge ionic compounds have complex, long chain molecules.
KI
CaCl2
Bai2
X+ Y-