Which of the following is used for deflouridation of water?

Ans: a (Alum and lime) Ref: Park, 19ed,p. 512The recommended level of flouridcs in drinking water in India is accepted as 0.5- 0.8 mg/L.The toxic manifestations of flourosis comprise the following:Dental flourosis-Characterised by ''mottling "of dental enamel, which has been reported at levels > 1.5 mg/1 intake.This is the early sign of dental flourosis. Mottling is best seen on the incisors of the upper jaw. It is almost entirely confined to permanent teeth and develops only during the period of formation.Skeletal flourosis:This is associated with lifetime daily intake of 3.0 to 6.0 mg/1Genu valgum: A new form of flourosis characterised by genu valgum and osteoporosis of the lower limbs in recent years.Intervention:Changing of water source: Running surface water contains lower quantity of flourides than ground water.Chemical treatment:Nalgonda technique for deflouridisation of water. It involves the addition of two chemicals (viz. lime and alum) in sequence followed by flocculation, sedimentation, and filtration.(The Nalgonda technique was developed by the National Environmental Engineering Research Institute ( NEERI, Nagpur.)