Bleaching powder is added to drinking water mainly for which purpose in water treatment?

Introduction / Context:
Safe drinking water is essential for public health, and various chemicals are used in water treatment to remove contaminants and kill harmful organisms. Bleaching powder, which contains calcium hypochlorite, is one such chemical often used in controlled amounts. This question asks you to identify the main purpose for adding bleaching powder to drinking water, focusing on its role in disinfection.

Given Data / Assumptions:

• Chemical considered: bleaching powder, usually calcium hypochlorite.
• Application: addition to drinking water.
• Options include disinfectant, antibiotic, coagulant, and antiseptic roles.

Concept / Approach:
Bleaching powder releases chlorine when added to water. Chlorine is a strong oxidizing agent that can kill bacteria, viruses, and other microorganisms present in water. In water treatment, chemicals that kill or inactivate disease causing microbes are called disinfectants. Antibiotics and antiseptics are related to medicine and topical applications, not directly to water treatment, and coagulants are used for particle removal, not primarily for killing germs. Therefore, the correct purpose is disinfection.

Step-by-Step Solution:
Step 1: Recall that bleaching powder is used to chlorinate water by releasing chlorine or hypochlorite ions. Step 2: Understand that chlorine reacts with and destroys many harmful microorganisms, making water safer to drink. Step 3: Recognize that a chemical that kills microbes in water is acting as a disinfectant. Step 4: Compare this with the meanings of antibiotic, coagulant, and antiseptic and see that these terms do not primarily describe water disinfection. Step 5: Select disinfectant as the main purpose of adding bleaching powder to drinking water.

Verification / Alternative check:
Water supply agencies commonly monitor residual chlorine levels after bleaching powder or other chlorination methods to ensure that disinfection has been effective. This practice would not make sense if bleaching powder were mainly used as an antibiotic or coagulant. Textbooks and public health guidelines consistently describe bleaching powder as a disinfecting agent for water. These references confirm that its main role is to kill or inactivate microorganisms, not to treat human infections directly or to serve as a coagulant.

Why Other Options Are Wrong:
Option B, antibiotic, refers to drugs used inside the body to treat bacterial infections, which is different from disinfecting water. Option C, coagulant, describes substances like alum that cause suspended particles to clump together and settle, a different step in water treatment. Option D, antiseptic, refers to agents applied to skin or living tissue to prevent infection, not primarily to treat large volumes of drinking water. None of these options matches the main role of bleaching powder in water treatment.

Common Pitfalls:
Students sometimes confuse terms like disinfectant, antiseptic, and antibiotic because all are related to controlling germs. Another pitfall is to associate bleaching powder only with whitening clothes and forget its role in water chlorination. To avoid these errors, remember that disinfectants are used on non living surfaces or in water, antiseptics are used on living tissues, and antibiotics are medicines taken into the body. Bleaching powder in water is clearly used as a disinfectant.

Final Answer:
Bleaching powder is added to drinking water mainly as a disinfectant, to kill disease causing microorganisms.