## **Core Concept**
The process of chlorination of water involves the addition of chlorine to water to disinfect it. The disinfecting action of chlorine is primarily due to the formation of certain compounds that are effective against microorganisms. Chlorine can react with water to form hypochlorous acid, which is a strong disinfectant.

## **Why the Correct Answer is Right**
The correct answer, , is right because when chlorine is added to water, it reacts with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl). The hypochlorous acid (HOCl) is a powerful disinfectant that can easily penetrate the cell walls of microorganisms, thereby killing them. The reaction is as follows: Cl2 + H2O → HOCl + HCl. HOCl is a more effective disinfectant than the hypochlorite ion (OCl-), which also forms but to a lesser extent and is pH-dependent.

## **Why Each Wrong Option is Incorrect**
- **Option A:** - This option is incorrect because although Cl2 (chlorine gas) does have disinfectant properties, the question specifically asks about the formation of a compound during the chlorination process that provides the disinfecting action.
- **Option B:** - This option is incorrect because while HCl (hydrochloric acid) is indeed formed during the reaction of chlorine with water, it does not have significant disinfectant properties compared to HOCl.
- **Option D:** - This option is incorrect because OCl- (hypochlorite ion) does have disinfectant properties but is less effective than HOCl, especially at lower pH levels where HOCl predominates.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the effectiveness of chlorination as a method of water disinfection largely depends on the formation of hypochlorous acid (HOCl), which is most effective at a pH range of 6.5 to 7.5. Outside this range, especially at higher pH levels, the formation of the less effective OCl- increases.

## **Correct Answer:** .