Chlorine water on standing loses its color and forms:

Chlorine water loses it's yellow color on standing in sunlight because it forms mixture of hypochlorous acid $( HOCl )$ and hydrochloric acid \left(HCl\right)$.</p><p>$C{l}_{2} ( g )$Is soluble in${H}_{2}O$and form chlorine water, in presence of sunlight as<br /><br />$C{l}_{2}\left(g\right) + {H}_{2}O \to HCl + HOCl$</p><p>This is a disproportionation reaction., where chlorine changes it's oxidation state from zero in${Cl}_{2}$to -1 in$HCl$and +1 in$HOCl. Hypochlorous acid formed in this reaction gives nascent oxygen which is responsible for bleaching action