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Question:

The method used to remove temporary hardness of water is:

Calgon's method

Clark's method

Ion-exchange method

Synthetic resins method

Solution:

Correct option is B. Clark's method. Clark's method is used to remove the temporary hardness of water, in which bicarbonates of calcium and magnesium are reacted with slaked lime Ca(OH)2.
Ca(HCO3)2+Ca(OH)2 → 2CaCO3↓+2H
Mg(HCO3)2+2Ca(OH)2 → 2CaCO3↓+Mg(OH)2↓+2H
Hence, option B is correct.