Which of the following is the most commonly used disinfectant in water purification ? 

The correct answer is Chlorine.

Key Points

• Chlorine is the most commonly used disinfectant in water purification.
• It is highly effective at killing a wide range of pathogens including bacteria, viruses, and protozoans.
• Chlorine can be easily applied and managed in water treatment processes.
• It is relatively inexpensive compared to other disinfectants.
• Chlorine not only disinfects but also helps in controlling odors and removing unwanted tastes from water.
• When added to water, chlorine forms hypochlorous acid (HOCl) and hypochlorite ion (OCl-), which are the active agents in disinfection.

 Additional Information

• Ozone
  • Ozone is another disinfectant used in water treatment but it is less common than chlorine.
  • It is a powerful oxidizing agent and can effectively kill bacteria and viruses.
  • However, ozone is more expensive and requires complex equipment to generate and apply.
  • Ozone decomposes quickly and does not provide a residual effect in the water, necessitating the use of additional disinfectants.
• Mercury
  • Mercury is a toxic heavy metal and is not used as a disinfectant in water treatment.
  • Exposure to mercury can cause serious health issues including neurological damage.
• Nitrogen
  • Nitrogen is a common element but it is not used as a disinfectant in water treatment.
  • Nitrogen is essential for plant growth and is often found in fertilizers, but it does not have disinfecting properties.