Final answer:
The correct whole number coefficient of chlorine is 2 when referring to its elemental form, denoted as Cl2, but typically is 1 when referring to the oxidation state in compounds like NaCl.
Step-by-step explanation:
The correct whole number coefficient of chlorine when it exists in its elemental form is 2, as chlorine is a diatomic molecule. This can be denoted as Cl2. In its molecular form in compounds, chlorine does not have a coefficient unless specified by a chemical equation, in which case you would use stoichiometry to determine it. However, if the question refers to the oxidation state or the combining capacity of a chlorine atom in a compound, it would typically have a coefficient of 1, as chlorine usually has an oxidation state of -1 (e.g., in NaCl).