Residual chlorine in chlorination of water should be-: (A) 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
Answer is B. Ans. is 'b' i.e., 0.5 mg/I, afterl hr