Multiple choice general knowledge science & technology

Permanent hardness of water may be removed by the addition of

  1. sodium carbonate

  2. alum

  3. potassium permanganate

  4. lime
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A Correct answer
Explanation

Sodium carbonate (washing soda, Na2CO3) removes permanent hardness by precipitating calcium and magnesium salts as insoluble carbonates. Lime (Ca(OH)2) only removes temporary hardness. Alum is used for water coagulation, not hardness removal, and potassium permanganate is a disinfectant/oxidizing agent.

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