Solution :
When chlorine react with water it gives nascent oxygen which bleaches the coloured substances.
$${H_2}O + C{l_2} \to 2HCl + \left[ O \right]$$
Coloured substance $$ + \left[ O \right] \to $$ Colourless substance
Releted MCQ Question on Inorganic Chemistry >> P - Block Elements
Releted Question 1
The reddish brown coloured gas formed when nitric oxide is oxidised by air is