Why does copper (II) chloride has Roman numeral?

Copper(II) chloride has a Roman numeral because it indicates the oxidation state of the copper ion in the compound. Roman numerals are used in naming compounds to clarify which ion is being referred to, as some elements can have multiple oxidation states. In this case, the "II" indicates that copper has a +2 charge, distinguishing it from copper(I) chloride, where copper would have a +1 charge. This system helps prevent confusion in chemical nomenclature.