Minimum chlorine content of water after chlorination should be ?: (A) 0.5mg\/L, (B) 5 mg\/L, (C) 0.05mg\/L, (D) 50mg\/L
Answer is A. park's textbook of preventive medicine 23rd edition *principle of chlorination is to ensure that a "free"residual chlorine of 0.5 mg/litre at end of one hour contact .