A sample of water has calcium content of 60 mg/l as CaCO\(_3\) and magnesium content of 80 mg/l as CaCO\(_3\). What is the total hardness of water?
DSSSB JE - 2023,
Answer: B
The total hardness of water is the sum of the calcium hardness and the magnesium hardness, both expressed as CaCO\(_3\):
\[ \begin{aligned} \text{Total hardness} = 60 + 80 \\ &= 140\ \text{mg/l as CaCO}_3 \end{aligned} \]The value 40 mg/l is the difference between the two, 200 mg/l is a sum with a wrong value for one of them, and 240 mg/l would result from adding an extra 100 mg/l. Since the data are already in CaCO\(_3\) equivalents, no conversion factor is needed.
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