Which of the following can be used to make drinking water free from germs?

Bleaching powder

The correct answer is option 3. Bleaching powder.

Bleaching powder, also known as calcium hypochlorite \((CaO_2Cl_2)\), is a chemical compound commonly used for disinfecting water. It is a strong oxidizing agent and has powerful disinfectant properties that make it effective at killing bacteria, viruses, and other harmful microorganisms in water.

When added to water, bleaching powder dissociates to release hypochlorite ions \((ClO^-)\) and calcium ions \((Ca^{2+})\). Hypochlorite ions are the active ingredient responsible for disinfection. They react with organic matter and microbial contaminants, such as bacteria and viruses, oxidizing them and rendering them harmless.

The disinfection process with bleaching powder is effective in killing a wide range of pathogens, including those responsible for waterborne diseases such as cholera, typhoid fever, and dysentery. It is commonly used for disinfecting drinking water supplies, particularly in situations where water quality is compromised or during emergencies such as natural disasters.

The dosage of bleaching powder required for water disinfection depends on factors such as the level of contamination, water temperature, and pH. It is important to follow recommended guidelines for proper dosing to ensure effective disinfection without compromising water quality or safety.

Overall, bleaching powder is a widely used and effective disinfectant for making drinking water free from germs, helping to ensure access to safe and potable water for communities around the world.