<prompt> Contact period of chlorination ?1 hour30 minutes1 12 hour2 hours  <response>: 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 mgL.Parks textbook of preventive and social medicine.K Park. Edition 23.Pg no: 715 