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Which salt is used to soften permanently hard water?

Answer and explanation

Correct answer: Washing soda

Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O. In water, it supplies carbonate ions that react with dissolved calcium and magnesium ions responsible for permanent hardness, forming insoluble carbonates that can be separated. For example, Ca²⁺ + CO₃²⁻ → CaCO₃(s). Hence option A is correct. Baking soda does not provide enough carbonate for this standard treatment, while Plaster of Paris and bleaching powder have different compositions and uses.

Related tags

ScienceClass 10Acids Bases SaltsWashing SodaPermanent HardnessAcidsBasesAnd SaltsAcids Bases And SaltsChemical Substances – Nature And Behaviour

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