Contact period of chlorination ?: (A) 1 hour, (B) 30 minutes, (C) 1 1\/2 hour, (D) 2 hours
Answer is A. Contact period for chlorination is one hour. The presence of free residual chlorine for a contact period of one hour is necesary to kill pathogens. The residual chlorine is 0.5 mg/L.Parks textbook of preventive and social medicine.K Park. Edition 23.Pg no: 715