Recommended contact period in chlorination -

Ans. is 'b' i.e., 1 hour Principles of chlorinationo Water should be clear and free of turbidity.o Chlorine demand of the water should be estimated, which is the amount of chlorine needed to destroy bacteria, oxidize all organic matter and neutrilize all ammonical substances present in water. The point at which the chlorine demand of water is met is called break point chlorination. If further chlorine is added beyond break point, free chlorine begins to appear in water