We’re being asked to determine the oxidation state or number in Cl- (chlorine ion) and Cl2 (chlorine gas).
The rules for oxidation states are as follows:
A. General Rules:
1. For an atom in its elemental form (Zn, Cl2, C(graphite), etc.) O.S. = 0
What are the oxidation numbers of 2Cl - and Cl2?