Water treatment: Purpose of adding alum during the purification of drinking water. Focus on the specific role alum plays in clarifying turbid water. Choose the correct purpose.

Given data

• Chemical: Alum (commonly aluminum sulfate).
• Process: Drinking water purification.

Concept/Approach
Alum is a coagulant. It destabilizes fine suspended particles, forming flocs that settle and clarify water.

Step-by-step reasoning
• Add alum → produces positively charged species in water. • These neutralize negatively charged colloids. • Particles aggregate into larger flocs → settle out during sedimentation.

Verification
Disinfection is typically achieved by chlorine/ozone/UV, not alum; pH control uses acids/alkalis; fluoride addition uses fluoride salts.

Common pitfalls
Assuming alum disinfects water — it does not; it clarifies by coagulation/flocculation.

Final Answer
Coagulation/flocculation of suspended impurities (to remove turbidity)