The minimum recommended concentration of free chlorine in drinking water at the end of one hour (mg/L) is -: (A) 0.1, (B) 0.5, (C) 1, (D) 1.5
Answer is B. The minimum recommended amount of residual chlorine is 0.5 mg/L. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 774