Question

Which gas is used to disinfect water?

• A. Nitrogen
• B. Hydrogen
• C. Chlorine
• D. Carbondioxide

Hint:

Chlorine is the most common water disinfectant because it: (1) kills pathogens effectively, (2) provides residual protection, (3) is economical. Swimming pools also use chlorine to maintain hygiene.

Answer 1

The Correct Option is C

Water disinfection is the process of eliminating harmful microorganisms (bacteria, viruses, protozoa) from water to make it safe for drinking. Why Chlorine is Used for Water Disinfection:

Powerful Oxidizing Agent: Chlorine kills bacteria and viruses by oxidizing their cell walls and disrupting their metabolic processes
Residual Effect: Chlorine remains in water for some time, providing continued protection against recontamination
Cost-Effective: Relatively inexpensive compared to other disinfection methods
Widely Used: Municipal water treatment plants worldwide use chlorine
Forms: Can be used as chlorine gas, sodium hypochlorite (liquid bleach), or calcium hypochlorite (tablets)
How Chlorine Works:

Reacts with water to form hypochlorous acid (HOCl) and hypochlorite ions (OCl⁻)
These penetrate bacterial cell walls and destroy enzymes and structures
Effective against bacteria (E. coli, cholera, typhoid), viruses, and some protozoa
Why Other Options are Incorrect:

(A) Nitrogen: Nitrogen is an inert gas that makes up 78% of air. It has no disinfecting properties
(B) Hydrogen: Hydrogen is highly flammable and not used for disinfection. Hydrogen peroxide (H₂O₂) has some disinfectant properties, but hydrogen gas does not
(D) Carbon dioxide: CO₂ is used in carbonated drinks and fire extinguishers. It does not kill microorganisms
Other Water Disinfection Methods:

Boiling
UV radiation
Ozone treatment
Iodine tablets
Filtration
Final Answer: Chlorine