The process used in domestic water softening, where sodium ion form a cationic exchange resin replace the calcium & magnesium ion reducing the hardness of water is done by :
MH SET - 2018, SET Exam - 2018,
Answer: A
The process is ion-exchange.
In a domestic water softener, hard water passes through a cation exchange resin charged with sodium ions. The resin takes up the calcium and magnesium ions that cause hardness and releases sodium in their place:
\[ \mathrm{2R{-}Na + Ca^{2+} \rightarrow R_{2}Ca + 2Na^{+}} \]
When the resin is exhausted it is regenerated with brine. Sand filtration and sedimentation remove suspended solids, not dissolved ions, and chlorination disinfects the water; none of them reduces hardness.
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