Question

If a sample of hard water contains $68$ ppm of $CaS{O}_4$, then the hardness of the same sample of water is:

• A. $68$
• B. $100$
• C. $200$
• D. $50$

Answer 1

The correct option is D $50$

In $136$ ppm of calcium sulphate, the degree of hardness is $100$.

So, in $68$ ppm of calcium sulphate, degree of hardness is $\frac{100}{136}\times 68=50$.

Option D is correct.