Which one of the following is used for water softening ?

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Mg(HCO3)2

Na3PO4

Na6P6O18

Na2HPO4

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Answer is Wrong!

This question was previously asked in

UPSC CAPF – 2019

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The correct answer is C, Na₆P₆O₁₈.

Na₆P₆O₁₈ is Sodium Hexametaphosphate, also known commercially as Calgon. It is a complex phosphate widely used as a water softening agent because it forms soluble complexes with calcium and magnesium ions, preventing them from precipitating and causing hardness.

Hard water contains high concentrations of dissolved minerals, particularly calcium (Ca²⁺) and magnesium (Mg²⁺) ions. Water softening aims to remove or neutralize these ions. Sodium salts like sodium hexametaphosphate sequester these ions, effectively “softening” the water. Sodium phosphate (Na₃PO₄) can also be used to precipitate hard ions, but hexametaphosphate is particularly effective due to its chelating ability.

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