Question:
Which of the following does NOT cause hardness of water?
Which of the following does NOT cause hardness of water?
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Hardness needs a soluble salt; carbonate of calcium is insoluble.
Updated On: Jun 24, 2026
- Calcium carbonate
- Calcium sulphate
- Calcium bicarbonate
- Magnesium bicarbonate
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Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Hardness of water is due to dissolved salts of calcium and magnesium. It is split into temporary and permanent hardness. Step 2: Temporary hardness is caused by dissolved bicarbonates - calcium bicarbonate and magnesium bicarbonate (options C and D) - and is removed by boiling. Step 3: Permanent hardness is caused by dissolved sulphates and chlorides such as calcium sulphate (option B), which is not removed by boiling. Step 4: Calcium carbonate is essentially insoluble in water, so it does not stay dissolved and therefore does not contribute to hardness - it is in fact the precipitate that forms when temporary hardness is boiled off. Hence calcium carbonate (option A) is the correct negative answer.
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