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Which of the following processes does NOT remove permanent hardness of water?

1. Permutit process
2. Synthetic resins method
3. Clark's method
4. Calgon's method

Correct answer: Clark's method

Solution

Clark's method involves adding calculated lime to precipitate Ca(HCO3)2 and Mg(HCO3)2 as CaCO3 and Mg(OH)2, targeting only bicarbonate salts; sulfate and chloride salts (permanent hardness) remain unaffected.

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