In the Stock system of nomenclature, the Roman numeral after the metal's name indicates what?

• A. The metal's oxidation state
• B. The metal's atomic number
• C. The metal's ionic charge
• D. The number of valence electrons

Answer: (C)

In this naming system, the Roman numeral after the metal name shows the metal’s oxidation state in that compound, which is the charge on the metal ion there. That numeral tells you how many electrons the metal has effectively lost or gained when forming the compound, i.e., its ionic charge in that context. For example, iron forms Fe2+ or Fe3+. In iron(III) chloride, the iron ion has a +3 charge, and the other ions provide the matching negative charges so the compound is neutral. So the numeral communicates the metal’s ionic charge in that specific compound. This isn’t about the atomic number, and it’s not a general statement about valence electrons—the numeral specifically encodes the charge state of the metal ion in the compound.