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': 'Compound used for water purification: \nSelect and explain. \nA. KMnO4, B. Iodine, C. Chlorine, D. Copper sulphate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans: c (Chlorine) Ref:Park, 19 ed,p. 575Xenodiagnosis is related to -trench feverEpidemiological tetrad is related to-scrub typhusChlorine:Contact period--1 hourNo effect on spores/ protozoal cyst needs superchlorinationEffective against all virus except polio & hepatitis ABleaching powder:Iodine:* Chemically CaOC12Emergency disinfection of water* Available chlorine is 33%Contact time 20-30 min* Unstable compoundEffective over wide range of pH values* Free residual chlorine needed for effective chlorination is 0.5 mg/1. at the end of one hour contact period.Persist longer than chlorine', 'role': 'assistant'}]