The Roman numerals after the name of the iron cation indicates the charge on the iron cation.
When which contain metal ions capable of forming more than one kind of cation, the Roman numeral after the metal’s name indicates the charge.
Therefore, the iron cation in iron(II) chloride has a charge of ##2^+##, and the charge on the iron cation in iron(III) chloride has a charge of ##3^+”##.
In the image below, a solution of iron(III) chloride is on the left side and a solution of iron(II) chloride is on the right side.
