During chlorination of drinking water, the 'break-point chlorination' refers to the point at which:

• A The chlorine demand of the water is exactly met, with zero residual chlorine
• B Chlorine converts entirely to chloramines without free residual
• C The pH of water drops below 7.0 due to hypochlorous acid formation
• D All ammonia and organic nitrogen compounds are oxidized and free residual chlorine begins to appear in the water ✓

Explanation

Break-point chlorination is the minimum dose of chlorine required to oxidize all ammonia, reducing substances, and organic matter — beyond this point, any additional chlorine added produces free residual chlorine (HOCl/OCl−), which has superior germicidal action compared with combined chlorine (chloramines). The 'break point' represents the nadir of the chlorine residual curve before free chlorine begins to accumulate. This ensures bactericidal efficacy and provides the measurable free residual chlorine standard (0.2 mg/L at consumer end).

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.