When writing a formula for a compound having a transition metal in it, . it is sometimes necessary to use the Roman numeral as the assigned charge of the metal

it is sometimes necessary to include a Roman numeral after the symbol of the metal

it is always necessary to include a Roman numeral after the symbol of the metal

it is always necessary to use the Roman numeral as the assigned charge of the metal

The correct option is;

It is always necessary to include a Roman numeral after the symbol of the metal

Explanation:

The transition metals can form ionic compounds with other elements by giving different number of electrons such that the transition metals can combine to form compounds in which they have different oxidation states

Therefore, in a compound formed by a transition metal, the value of the transition metal's valency or oxidation state in the compound is indicated by the inclusion of an equivalent Roman numeral after the transition metal in the name of the chemical formula of the compound