Which chemical substance is used for water purification?

Correct option is B

Sol. Bleaching Powder (Calcium Hypochlorite, Ca(OCl)₂) is widely used for water purification as it acts as a disinfectant by releasing chlorine when mixed with water. Chlorine kills bacteria, viruses, and other pathogens, making water safe for consumption. This method is commonly used in municipal water treatment and emergency water disinfection.
Explanation of each option:
· (a) Lime – Not primarily used for disinfection. Lime (Calcium Hydroxide) is mainly used for pH adjustment and hardness removal in water treatment plants but does not disinfect water effectively.
· (b) Bleaching Powder – Correct answer. It is used for disinfection, killing harmful microorganisms in water, and is commonly used in rural and urban water treatment plants.
· (c) Potassium Permanganate – Used for oxidation but not primary disinfection. It is sometimes used to remove iron, manganese, and organic matter but is not as effective as chlorine-based disinfectants.
· (d) Formaldehyde – Not used for water purification. It is mainly used as a preservative and disinfectant in medical settings but is toxic if ingested in drinking water.
Source: World Health Organization (WHO) and Bureau of Indian Standards (BIS) guidelines on drinking water purification.