The breakpoint in chlorination refers to the point at which:
Choose the correct answer
Chlorine demand is zero
All combined chlorine is destroyed and free chlorine residual begins to appear
Water becomes safe to drink
pH becomes neutral
Correct Answer
B. All combined chlorine is destroyed and free chlorine residual begins to appear
Why is this the answer?
When chlorine is added to water: first reacts with reducing substances; then forms combined residual (chloramines with NH3); then at breakpoint the residual drops (chloramines are destroyed by excess Cl2); beyond breakpoint only FREE chlorine residual remains. Free chlorine is stronger disinfectant. Breakpoint chlorination ensures free residual in distribution.
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