**Question:** During the process of chlorination of water, the disinfecting action of chlorine is due to the formation of -

A. Chloramine
B. Chlorine dioxide
C. Chlorite
D. Chlorine dioxide

**Core Concept:**
The process of chlorination is a common method used to disinfect water and kill bacteria, viruses, and other microorganisms. Chlorine is the most commonly used disinfectant in this process. When chlorine reacts with water, several compounds are formed, including chloramine, chlorine dioxide, chlorite, and hypochlorous acid. Among these, chlorine and chlorine dioxide are the most relevant for understanding the disinfecting action of chlorine in water purification.

**Why the Correct Answer is Right:**
The correct answer, D. Chlorine dioxide, is important because it is a highly effective oxidizing agent that can penetrate the cell walls and membranes of microorganisms, leading to the disruption of their cellular functions and ultimately causing death. In contrast, chloramine and chlorite are less potent oxidizing agents, which may not be as effective at disinfecting water. Hypochlorous acid is a short-lived intermediate, while chlorine dioxide is a stable compound that can remain in the water after the chlorination process, ensuring sustained disinfection.

**Why Each Wrong Option is Incorrect:**
A. Chloramine (NH2Cl + Cl2) is a compound formed when chlorine reacts with ammonia present in water. Although chloramine can have some antimicrobial activity, it is less potent than chlorine dioxide and is not as effective for disinfecting water.

B. Chlorine dioxide (ClO2) is another compound formed from chlorine when it reacts with water. Chlorine dioxide is a short-lived intermediate and may not contribute significantly to the overall disinfecting action of chlorine in water.

C. Chlorite (ClO2-) is another compound formed from chlorine when it reacts with water. Chlorite is less potent than chlorine dioxide and chloramine, making it less effective for water disinfection.

**Clinical Pearls:**
Chlorine dioxide remains the most effective compound for disinfecting water because of its potent oxidizing properties and stability. Disinfection of water involves the formation of various compounds, including chlorine dioxide. Maintaining the stability of chlorine dioxide in the water ensures sustained disinfection, which is crucial for ensuring safe drinking water and preventing waterborne diseases.