Question

Assertion (A): Fluorosis results, if $F^{-}$ ion concentration exceeds 3 ppm in drinking water.
Reason (R): Nalgonda technique requires lime and aluminum salts from drinking water.

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is not correct explanation of A
• C. A is true and R is false
• D. A is false and R is true

Answer 1

The correct option is B Both A and R are true but R is not correct explanation of A

Fluoride deficiency in drinking water is harmful and causes tooth decay. When fluoride concentration in water is greater than 3 ppm, it makes the enamel of teeth harder by converting hydroxy apatite $\left[3C{a}_3\right(P{O}_4\left)Ca\right(OH{)}_2]$, the enamel in the surface of teeth to fluorapatite, $\left[3C{a}_3\right(P{O}_4\left)Ca{F}_2\right]$.
The methods of removal of fluoride ions from drinking water are called defluoridation techniques.
Defluoridation techniques are as follows:
a) Ion exchange method: defluoron-1 and defluoron-2 synthetic resins are used to remove fluoride ions.
b) Nalgonda technique: bleaching powder, lime and alum are used to remove fluoride ions. The fluoride ions are precipitated as calcium aluminium fluoride.
c) Activated carbon method.

Both statements are independent.