In disinfection, which of the following forms of chlorine is most effective in killing the pathogenic bacteria?

HOCl (Hypochlorous Acid):

• Hypochlorous acid is the most effective disinfecting form of chlorine because it is a neutral molecule that easily penetrates the cell walls of microorganisms, including bacteria, viruses, and protozoa. Once inside the cell, it disrupts vital cellular processes, leading to the death of the organism.
• HOCl is produced when chlorine (Cl2) or sodium hypochlorite (NaOCl) is dissolved in water. It exists in equilibrium with the hypochlorite ion (OCl), but HOCl is more effective because it is more reactive and can diffuse more readily across cell membranes.

OCl (Hypochlorite ion):

• The hypochlorite ion is also a disinfectant, but it is less effective than HOCl because it is negatively charged and does not penetrate cell membranes as efficiently as HOCl.

NH₂Cl (Chloramine):

• Chloramine is used as a disinfectant, but it is less effective than free chlorine (HOCl and OCl) in killing bacteria. It is often used in water treatment where a longer-lasting disinfectant is needed, but it is slower-acting compared to HOCl.

Cl₂ (Chlorine gas):

• Chlorine gas, when dissolved in water, forms HOCl and OCl^-, but in its gaseous form, it is not directly effective as a disinfectant until it is dissolved and forms these active species.