Question

A water sample has ppm level concentration of following anions : 

F^- = 10; SO^2-₄ = 100; NO^-₃ = 50

The anion/anions that make/makes the water sample unsuitable for drinking is/are 

(a) Only NO^-₃ 

(b) Both SO^2-₄  and NO^-₃ 

(c) Only F^- 

(d) Only SO^2-₄ 

Answer 1

Correct Option (c) Only F^- 

Explanation:

NO^-₃ The maximum limit of nitrate (NO^-₃) in drinking water is 50 ppm and its source is fertilisers, lf the maximum limit is increased in water it will cause methemoglobinemia (blue baby syndrome)

SO^2-₄ Tne maximum limit of sulphate (SO^2-₄ ) according to WHO is 500 pm and its sources are acid rain, industries. Excess SO^2-₄ has laxative effect.

F^-  The maximum limit of fluoride (F^-) is about 1,5 ppm. lts higher concentration converts enamel to more harder fluorapatite. Concentration (> 2ppm) causes brown mottling of teeth and high concentration (> 10 ppm) are harmful for bones and teeth.

SO^2-₄  (100 ppm) and NO^-₃ (50 ppm) in water is suitable for drinking but the concentration of F^- (10 ppm) makes water unsuitable for drinking.