This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and Health, Subject name: Social & Preventive Medicine
[{'content': "Chlorine demand of water is measured by \nSelect and explain. \nA. Chlorimeter, B. Berkfield filter, C. Double pot method, D. Horrock's apparatus", 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e. Horrock's apparatus [Ref: Park 20/e, p 637 (19/e, p 577, 18/e, p 530)1Chlorine 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 ammonical 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.", 'role': 'assistant'}]