Permanent hardness of water can be removed by adding __________?
- A. Chlorine
- B. Washing soda
- C. Bleaching powder
- D. None of these
Explanation
Washing soda, sodium carbonate, removes permanent hardness by precipitating calcium and magnesium ions as insoluble carbonates. Boiling removes temporary hardness, but not the sulphates and chlorides responsible for permanent hardness.