Final answer:
The Roman numeral in a transition metal's name signifies the metal ion's charge, necessary for compounds with variable charges. For CuCl, the correct compound name is copper(I) chloride, indicating a +1 charge for copper.
Step-by-step explanation:
The purpose of a Roman numeral in the name of most transition metals is to indicate the charge of the metal ion when it has multiple possible charges. This system of naming is known as the Stock system and it helps to differentiate compounds that contain the same elements but in different proportions due to the variation in the oxidation state of the metal ion.
For CuCl, the correct Roman numeral to use is (I) to indicate copper with a +1 charge, as chlorine has a -1 charge. Thus, the correct name for CuCl is copper(I) chloride.
The purpose of a Roman Numeral in the name of most transition metals is to indicate the charge of the metal ion. Transition metals can form two or more cations with different charges, and to distinguish between them, the charge is specified using a Roman numeral in parentheses after the name of the metal. For example, iron can have a charge of either 2+ or 3+, so the compounds FeClâ‚‚ and FeCl3 are named iron(II) chloride and iron(III) chloride, respectively.
In the case of the compound CuCl, the correct name for it would be copper(I) chloride. This is because the charge on the copper ion is 1+.