16.Residual chlorine in water is determined by

17.The settling velocity of a particle in a sedimentation tank depends on

18.Assertion A: Slow sand filters are more efficient in removal of bacteria than rapid sand filters. Reason R : The sand used in slow sand filters is finer than that in rapid sand filters. Select your answer based on the coding system given below:

19.The length of rectangular sedimentation tank should not be more than

20.The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about