41) The amount of coagulant needed for coagulation of water increases with i)increase in turbidity of water ii)decrease in turbidity of water iii)increase in temperature of water iv)decrease in temperature of water The correct answer is

42) Alum as a coagulant is found to be most effective when pH range of water is

43) The detention period in coagulation tanks is usually kept as

44) The alum, when added as a coagulant in water

45) The chemical most commonly used to increase speed of sedimentation of sewage is