Assertion (A): Chlorine dioxide has certain advantages over free chlorine and hypochlorite in water disinfection. Reason (R): Chlorine dioxide is an unstable gas and does not combine with ammonia or other natural organics to produce chloramines or chloroform.
In the light of the above statements, choose the most appropriate answer from the options given below:

Correct option is A

Explanation of Assertion (A):
Chlorine dioxide (ClO2_22​) is widely recognized as an effective water disinfectant, particularly in comparison to free chlorine and hypochlorite. It is more efficient in inactivating pathogens like viruses and bacteria, including resistant microorganisms such as Cryptosporidium and Giardia. Unlike chlorine, it doesn’t produce harmful by-products like trihalomethanes (THMs) and chloramines during the disinfection process.
Explanation of Reason (R):
Chlorine dioxide is an unstable gas that does not interact with ammonia or natural organic matter to form chloramines or chloroform (a type of THM). This property makes it a safer and more effective alternative to chlorine and hypochlorite for water disinfection. Its instability is a reason why it must often be generated onsite.
Correlation:
The reason provided directly explains why chlorine dioxide has advantages over free chlorine and hypochlorite, as its chemical behavior prevents the formation of potentially hazardous by-products like chloramines and chloroform. Thus, both (A) and (R) are correct, and (R) is the correct explanation of (A).
Information Booster:
1. Key Advantages of Chlorine Dioxide:
· Effective against chlorine-resistant pathogens.
· Minimizes harmful by-products like THMs.
· Effective across a broad pH range (4–10).
2. Disadvantages of Chlorine Dioxide:
· Unstable and must be produced onsite.
· Higher operational costs compared to chlorine.
3. By-products of Chlorine:
· Free chlorine can react with organic matter to form THMs (e.g., chloroform) and chloramines, which are harmful.
4. Applications of Chlorine Dioxide:
· Used in municipal water disinfection, industrial water treatment, and pulp bleaching.
5. Comparison to Other Disinfectants:
· Chlorine dioxide is often preferred for specific applications due to its selective reactivity and efficacy.