The compound which on dissolution in water makes it hard, is
- ACaCO3
- BMgSO4
- CCa(HCO3)2
- DMore than one of the above
- ENone of the above
Show answer and explanation
Correct answer: (d) More than one of the above
Explanation
Water becomes hard when salts of calcium and magnesium dissolve in it:
- Temporary hardness comes from the bicarbonates, such as Ca(HCO₃)₂ and Mg(HCO₃)₂, and boiling removes it.
- Permanent hardness comes from the chlorides and sulphates, such as MgSO₄ and CaCl₂, and boiling does not remove it.
CaCO₃ hardly dissolves in water, so both MgSO₄ and Ca(HCO₃)₂ make water hard: "More than one of the above".