Water treatment (permanent hardness): Which method <em>cannot</em> remove <strong>permanent hardness</strong> due to Ca/Mg chlorides/sulfates? Identify the technique ineffective against non-bicarbonate hardness. Choose the correct option.

Given data

• Permanent hardness arises from Ca/Mg chlorides and sulfates.

Concept/ApproachBoiling removes temporary hardness (bicarbonates) by decomposing HCO₃⁻ to CO₃²⁻/CO₂. It does not remove chlorides/sulfates. Washing soda (Na₂CO₃) precipitates CaCO₃; distillation removes all salts; NaOH can precipitate Mg(OH)₂ and assist softening in appropriate processes.

Final AnswerBoiling