This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
Which pa of chlorine disinfection is most effective?- 
Select and explain. 
A. Hypochlorous acid, B. Hypochlorous ion, C. Hypochlorite ion, D. None
A: Hypochlorous acid
Answer: A: Hypochlorous acid 
Explanation: The disinfecting action of chlorine is mainly due to hypochlorous acid. It is 70-80 times effective than hypochlorite ion. So chlorine acts as best disinfectant a when pH of water is around 7 because of the predominance of hypochlorous acid. (PARK TB 25th edition pg 774)