Which one of the following methods can be used to remove permanent hardness of water ?

Water hardness is classified into temporary and permanent types. Temporary hardness, caused by calcium and magnesium bicarbonates, can be removed by simple boiling, which precipitates them as carbonates [1]. Permanent hardness is caused by dissolved chlorides, nitrates, and sulfates of calcium and magnesium [1]. This form of hardness cannot be removed by boiling [1]. Instead, it requires chemical treatments or specialized processes. The ion-exchange method is a highly efficient and widely used technique for removing permanent hardness. In this process, hard water passes through a resin bed or zeolite column where calcium and magnesium ions are exchanged for sodium ions, effectively softening the water [1]. While lime treatment (lime-soda process) can also address permanent hardness when combined with soda ash, ion-exchange is a primary standalone method specifically cited for this purpose [2].

Sources

1. [1] https://www.bharathuniv.ac.in/colleges1/downloads/courseware_ece/notes/1%20BCH101%20%20-%20chemistry%201%20-%20NOTES.pdf
2. [2] https://www.griet.ac.in/nodes/EC_UNIT_1.pdf