Iron (II) nitrate and iron (III) nitrate?

Roman numeral is required to specify the charge on the cation. The charge on a cation is typically +1, +2, or +3. The majority of metals have a cation with a +2 charge, although some can exist in different forms. For example, iron exists as both a +2 and a +3 cation. The characteristics of the +2 and +3 form are slightly different. Iron nitrate can be found as iron (II) nitrate or iron (III) nitrate, the former being green in color while the latter is pale violet.