Hardness of water is caused by dissolved salts of:
Choose the correct answer
Sodium and potassium
Calcium and magnesium ions
Iron and manganese
Fluoride and chloride
Correct Answer
B. Calcium and magnesium ions
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Hardness is caused by Ca²⁺ and Mg²⁺ ions. Their bicarbonates (HCO3⁻) cause temporary hardness (removed by boiling). Their sulphates, chlorides, and nitrates cause permanent hardness (requires lime-soda or ion exchange). Hard water wastes soap, deposits scale in boilers (CaCO3 and Mg(OH)2 precipitate at high temperature).
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