Question

A water sample has ppm level concentration of following anions
$F^{-}=10;S{O}_4^{2-}=100;N{O}_3^{-}=50$
The anion/anions that make/makes the water sample unsuitable for drinking is/are:

• A. both $S{O}_4^{2-}$ and $N{O}_3^{-}$
• B. only $F^{-}$
• C. only $S{O}_4^{2-}$
• D. only $N{O}_3^{-}$

Answer 1

Answer: (B)

only $F^{-}$

$N{O}^{-3}$ The maximum limit of nitrate $N{O}^{-3}$ 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) $S{O}_4^{2-}$. The maximum limit of sulphate ($S{O}_4^{2-}$ ) according to WHO is 500 pm and its sources are acid rain, industries. Excess $S{O}_4^{2-}$ 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. $S{O}_4^{2-}$ (100 ppm) and $N{O}^{-3}$ (50 ppm) in water is suitable for drinking but the concentration of $F^{-}$ (10 ppm) makes water unsuitable for drinking.

Hence, the correct option is B.