Final answer:
Chlorine has its lowest oxidation state of -1 as the chloride ion (Cl-) in compounds such as sodium chloride (NaCl). In the given options, chlorine is in the lowest oxidation state when its oxidation state is -1.
Step-by-step explanation:
The student has asked which substance has chlorine in the lowest oxidation state. The oxidation state of chlorine varies in different compounds. For example, in perchloric acid (HClO4), chlorine has an oxidation state of +7, which is its maximum, while in the compound Cl- (chloride ion), chlorine has its lowest possible oxidation state of -1.
Reviewing the provided information, it indicates that when oxychlorine (OCl-) is reduced to chloride (Cl-), the oxidation state of chlorine goes from +1 to -1. This signifies that in these chemical reactions, the lowest oxidation state for chlorine is -1, present as the chloride ion (Cl-).
Therefore, in the compounds presented, the substance in which chlorine has its lowest oxidation state would be the chloride ion, Cl-, as in the case of, for example, sodium chloride (NaCl), where chlorine exists as Cl-.