How do Roman numerals in names such as iron(II) chloride and iron(III) chloride show oxidation states?

In the nomenclature of inorganic chemistry, Roman numerals are used to specify the oxidation state of an element that can exist in more than one state within a compound.12

Because certain elements—particularly transition metals—can donate or acquire varying numbers of electrons when forming chemical bonds, they may exhibit multiple oxidation states. The Roman numeral, placed in parentheses after the name of the element, explicitly indicates the specific oxidation number of that metal ion in the compound.132

For example:
* Iron(II) chloride (FeCl₂): The (II) indicates that the iron atom is in a +2 oxidation state.1
* Iron(III) chloride (FeCl₃): The (III) indicates that the iron atom is in a +3 oxidation state.12

This system ensures clarity in naming, as it distinguishes between different compounds formed by the same elements by identifying the specific charge or bonding capacity of the metal cation involved.45