Water treatment (hardness): Permanent hardness of water can be removed by adding which chemical? Target the sulfate/chloride salts of Ca/Mg (non-carbonate hardness). Choose the correct reagent.

What is being asked?
The reagent that removes permanent hardness (Ca/Mg chlorides/sulfates) by precipitation.

Given data

• Permanent hardness ≠ carbonate hardness

Concept/Approach
Na₂CO₃ reacts with Ca²⁺/Mg²⁺ to form insoluble carbonates (CaCO₃, MgCO₃), thus softening the water. Lime mainly addresses temporary hardness by precipitating carbonates from bicarbonates.

Final Answer
Washing soda (sodium carbonate, Na₂CO₃)