When chlorine water is exposed to diffused sunlight, it evolves colourless and odourless oxygen gas.
When chlorine water is exposed to sunlight, it loses its characteristic light yellow colour and becomes colourless. The presence of sunlight forms an intermediate product of hypochlorous acid, which further reacts to form hydrochloric acid in more concentrated form and nascent oxygen. The nascent oxygen further reacts to form molecular oxygen.
Cl2 + H2O → HClO + HCl