Concept:Chlorine water bleaches by an oxidation reaction.Explanation:Chlorine reacts with water to form hydrochloric acid and hypochlorous acid:Cl2+H2O⇌HCl+HOClThe hypochlorous acid, HOCl, is a strong oxidizing agent.It oxidizes coloured materials into colourless compounds.Hence, chlorine water acts as a bleaching agent because it is an oxidizing agent.Answer:C. An oxidizing agent