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 $F^{-}$
• B. only $SO_4^{2-}$
• C. only $NO_4^{2-}$
• D. only $SO_4^{2-}$ and $NO^{-}_3$

Answer 1

The Correct Option is A

To determine which anions make the water sample unsuitable for drinking, we must compare the given concentration levels with the permissible limits set by health authorities such as the World Health Organization (WHO) and other public health standards.

1. Analyzing $F^{-}$ (Fluoride):
   • The WHO guideline for fluoride concentration in drinking water is 1.5 ppm.
   • Here, the water sample has a fluoride concentration of 10 ppm, which exceeds the permissible limit.
   • High levels of fluoride can lead to dental and skeletal fluorosis, making the water unsuitable for drinking.
2. Analyzing $SO_4^{2-}$ (Sulfate):
   • The typical standard for sulfate in drinking water is around 250-500 ppm, depending on the country.
   • The concentration of sulfate in this sample is 100 ppm, which is well within the permissible range and is considered safe.
3. Analyzing $NO_3^{-}$ (Nitrate):
   • The WHO recommendation for nitrate in drinking water is a maximum of 50 ppm.
   • The nitrate concentration here is 50 ppm, which is just at the limit set by WHO, but not exceeding it.
   • While this level requires monitoring, it is still within acceptable limits and not immediately unsafe.

Based on this analysis, only the fluoride concentration exceeds the permissible limits, making the water sample unsuitable for drinking.

Thus, the correct answer is: only $F^{-}$