This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment, Subject name: Social & Preventive Medicine
In chlorination of water, the main disinfecting action is due to:- 
Select and explain. 
A. Hydrogen ions, B. Hydrochloric acid, C. Hypochlorous acid, D. Chloride ions
C: Hypochlorous acid
Answer: C: Hypochlorous acid 
Explanation: Chlorination of water: - Used for large scale purification of water & for drinking water. Disinfection action of chlorine in water is due to: Hypochlorous acid - major role in disinfection (HOCl). Hypochlorite ions - minor role in disinfection. Chloride has residual germicidal effect. It kills bacteria, many viruses but not spores . It oxidizes iron, manganese & hydrogen sulphide. It also destroys taste & odorproducing components. Chlorine acts best as a disinfection for water at: pH around 7.0