Which one of the following methods can be used to remove permanent hardness of water ?
Boiling
Ion-exchange
Lime treatment
Bubbling sulphur dioxide gas
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This question was previously asked in
UPSC CAPF – 2020
Permanent hardness in water is caused by dissolved sulfates and chlorides of calcium and magnesium, which do not precipitate out upon boiling. The ion-exchange method, using materials like zeolite or synthetic resin, replaces the hard ions (Ca2+, Mg2+) with soft ions (usually Na+). This process is effective in removing both temporary and permanent hardness.