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Which one of the following substances is absent in clear hard water?

1. MgCO3
2. MgSO4
3. Mg(HCO3)2
4. CaCl2

Correct answer: MgCO3

Solution

MgCO3 is not present in clear hard water because hard water typically contains soluble salts like MgSO4, Mg(HCO3)2, and CaCl2, while MgCO3 is less soluble and often precipitates out.

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