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: Unknown
[{'content': 'Which part of chlorine disinfection is most effective? \nSelect and explain. \nA. Hypochlorous acid, B. Hypochlorousion, C. Hypochlorite ion, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Chlorination is one of the greatest advances in water purification.\n\nChlorine kills pathogenic bacteria, but has no effect on spores, certain viruses (e.g., polio, viral hepatitis) and cyst of E. histolytica, in usual doses.\n\xa0\nMechanism of action\n\nWhen chlorine is added to water, there is formation of hypochloric and hypochlorous acid\n\nThe hypochloric acid is neutralized by the alkanity of the water.\n\nThe hypochlorous acid ionizes to form hydrogen ions and hypochlorite ions.\n\nThe disinfecting action of chlorine is mainly due to the hypochlorous acid and to a small extent due to the hypochlorite ions.\nThe hypochlorous acid is the most effective form of chlorine for water disinfection, it is 70-80 times more effective than hypochlorite ion.\n\xa0\nMethod of Chlorination\n\nFor disinfecting large bodies of water, following methods of chlorination are available:\n\n1. Chlorine gas → First choice\n\xa0\nChloramine\nPerchloron or high test hypochlorite (HTH)', 'role': 'assistant'}]