Question

when is a roman numeral most likely needed in the name of an ionic compound? when more than one polyatomic ion appears when the anion is a polyatomic ion when more than one cation is used in the formula when the cation is a transition metal

Explanation:

Transition metals can have multiple oxidation states. Roman numerals are used in the names of ionic compounds to indicate the oxidation state of the transition - metal cation. For example, in FeCl₂, iron has an oxidation state of + 2, and it is named iron(II) chloride. Other situations mentioned do not require indicating oxidation state with Roman numerals in the same way.

Answer:

when the cation is a transition metal