Which one of the following methods can be used to remove permanent har

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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Answer is Wrong!

This question was previously asked in

UPSC CAPF – 2020

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The Ion-exchange method can be used to remove permanent hardness of water.

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.

A) Boiling removes only temporary hardness (caused by bicarbonates). C) Lime treatment primarily removes temporary hardness by precipitating calcium and magnesium bicarbonates. Adding lime and soda ash (lime-soda process) can remove both. D) Bubbling sulfur dioxide gas through water forms sulfurous acid, which does not effectively remove the ions responsible for permanent hardness and is not a standard water softening method.

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