Question

A water sample has ppm level concentration of the following anions ${F^ - } = 10$, $SO_4^{2 - } = 100$, $NO_3^ - = 50$
The anion/ anions that make/makes the water sample unsuitable for drinking is/ are:
A. both $SO_4^{2 - }$and $NO_3^ -$
B. only ${F^ - }$
C. only $SO_4^{2 - }$
D. only $NO_3^ -$

Answer 1

Hint: The given ions fluorine ion, sulfate ion and nitrate ion can be present in drinking water in some quantity. There are some limits set by the Word health organization about the concentration of ions in ppm to be present so that the water is suitable for drinking.

Complete step by step answer:
The given anions are fluorine ion ${F^ - }$, sulfate ion $SO_4^{2 - }$, nitrate ion $NO_3^ -$.
The given water sample contains fluorine ion with ppm value 10, sulfate ion with ppm value 100 and nitrate ion with ppm value 50.
The maximum limit of nitrate ion to be present in the drinking water is 50 ppm. If the maximum limit for the concentration of nitrate ion in the drinking water exceeds it will cause methemoglobinemia which is also known as blue baby syndrome.
The maximum limit of sulfate ion set by the Word Health organization WHO is 500 ppm. When the concentration of the sulfate ion in the drinking water exceeds it causes a laxative effect.
The maximum concentration of the fluorine ion is 1.5 ppm, the higher concentration of fluorine ion converts enamel to fluorapatite which is harder. The concentration greater than 2ppm leads to brown mottling of teeth and even high concentration up to or more than 10 ppm are dangerous for bones and teeth.
The concentration of sulphate ion which is 100 ppm and the concentration of nitrate ion which is 50 ppm present in the drinking water is suitable for drinking but the concentration of fluorine ion which is 10 ppm will make water unsuitable for drinking.
Therefore, the correct option is B.

Note:
The source of nitrate ion is fertilizers which are present in the soil. The source of sulfate ions is acid rain, industries. Fluoride ions are present in traces in water from minerals like fluorite.