Water treatment (hardness): Removing permanent hardness of water by chemical addition. Select the compound that effectively removes Ca²⁺/Mg²⁺ hardness by precipitation. Choose the correct reagent.

Given data

• Permanently hard water contains Ca²⁺/Mg²⁺ (as chlorides/sulfates).

Concept/Approach
Adding sodium carbonate (washing soda) precipitates CaCO₃/MgCO₃, removing hardness ions from solution.

Step-by-step
• CaCl₂ + Na₂CO₃ → CaCO₃↓ + 2 NaCl • MgSO₄ + Na₂CO₃ → MgCO₃↓ + Na₂SO₄

Common pitfalls
Chlorine/bleaching powder disinfect; KMnO₄ is an oxidant, not a hardness remover.

Final Answer
Washing soda (Na₂CO₃)