Which of the following is/are NOT active disinfectant(s) in water treatment?

OH (hydroxyl radical)
O3 (ozone)
OCl− (hypochlorite ion)
Cl− (chloride ion)

Correct answer: Cl− (chloride ion)

Solution

The chloride ion (Cl−) is not an active disinfectant because it does not possess the oxidative properties necessary to kill pathogens, unlike the other options which are effective in disinfection processes.

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