Which one of the following method is used for the estimation of the chlorine demand of water?

Ans. is 'b' i.e. Horrock's apparatus Chlorine demand of water can be estimated by Horrock's apparatus.Chlorine demand of water is the amount of chlorine that is needed to destroy bacteria, and to oxidize all the organic matter and ammoniacal substances present in water.It is the difference between the amount of chlorine added to the water, and the amount of residual chlorine remaining at the end of a specific period of contact (usually 1 hr), at a given temperature and pH of water.Berkefield filter is a type of ceramic filter which is used for purifying water on small scale.The Double Pot Method provides a constant dose of chlorine to well water during periods of emergency.