Which gas is passed in the water to kill bacteria?

The correct answer is Chlorine.

Key Points

• Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules.
  • Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells.
  • When enzymes come in contact with chlorine, one or more of the hydrogen atoms in the molecule are replaced by chlorine.
  • This causes the entire molecule to change shape or fall apart.
  • When enzymes do not function properly, a cell or bacterium will die.
  • Chlorine effectively kills a large variety of microbial waterborne pathogens, including those that can cause typhoid fever, dysentery, cholera and Legionnaires' disease. 

Additional Information

• Bromine is a chemical element with the symbol Br and atomic number 35. Bromine is used in many areas such as agricultural chemicals, dyestuffs, insecticides, pharmaceuticals and chemical intermediates.
• Iodine is an essential mineral commonly found in seafood.
• A colourless, odourless gas Nitrogen is important to the chemical industry.
  • It is used to make fertilisers, nitric acid, nylon, dyes and explosives.
  • To make these products, nitrogen must first be reacted with hydrogen to produce ammonia.