This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'Residual chlorine in chlorination of water should be- \nSelect and explain. \nA. 1 mg// after 1 hr, B. 0.5 mg/1 after 1 hr, C. 1 melt after 30 mins, D. 0.5 mg/1 after 30 mins', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 0.5 mg/I, afterl hr", 'role': 'assistant'}]