Question

The cheapest method for the defluoridation is :
A. Activated carbon method
B. Ion exchange method
C. Nalgonda technique
D. Electrolytic method

Answer 1

Hint: The methods of removal of fluoride ions from drinking water are called the defluoridation techniques. The cheapest method of defluoridation is the most economically preferred method among the users.

Step by step answer:
Among the following techniques which are mentioned for the defluoridation, Nalgonda technique is the cheapest method. For the defluoridation in case of the Nalgonda technique bleaching powder, lime and alum are used to remove the fluoride ions. The fluoride ions are precipitated as a calcium aluminium fluoride. Activated charcoal can absorb organic substances like DDT and Endrin.
Therefore the answer to the question is which is the cheapest method of defluoridation, the answer is Nalgonda technique.
So, the correct answer is Option C.

Additional Information:
Activated carbon also called activated charcoal is a form of carbon process to have low volume pores that increases surface area available for adoption or chemical reaction. Further chemical treatment often enhances absorption properties. Activated carbon is usually derived from charcoal.
Ion exchange is a water treatment method where one or more undesirable ionic contaminants are removed from water by exchange with another non objectionable or less objectionable ionic substance.
Electrolysis is a method of separating bonded elements and compounds by passing an electric current through them; it uses a direct electric current to drive an otherwise non-spontaneous chemical reaction. Electric current is carried by electrons in the external circuit.

Note: In Nalgonda technique there is an addition of aluminium salts, slime and bleaching powder which is followed by rapid mixing, flocculation, sedimentation, filtration and disinfection.