Final answer:
The correct IUPAC name for Cl⁻ is 'chloride ion', following the convention of using the element stem plus '-ide' and the word 'ion' for monatomic anions.
Step-by-step explanation:
The proper IUPAC name for the compound Cl⁻ is the chloride ion. In naming a monatomic anion, we use the stem of the element name followed by the suffix '-ide' and then add the word 'ion'. Therefore, Cl⁻ is designated as "chlor-" + "-ide ion," resulting in the name 'chloride ion'. This naming rule is consistent with other monatomic anions like O²⁻ becoming the 'oxide ion' and Se²⁻ becoming the 'selenide ion'. When naming molecular compounds similarly, we connect the name of the first element with the modified name of the second element, which gets the '-ide' suffix, like in carbon tetrachloride (CCl₄).