Which of the following is NOT used to disinfect water?

Fluorine is not used to disinfect water. Instead, it is primarily known for its role in dental health, specifically in the prevention of tooth decay. Fluorine compounds, such as sodium fluoride, are added to drinking water for this purpose.

In contrast, chlorine, bromine, and iodine are all effective disinfectants used to kill pathogens in water. Chlorine is the most widely used disinfectant in water treatment processes because it is effective, inexpensive, and provides residual disinfection. Bromine is also used, particularly in hot tubs and swimming pools, as it works in higher water temperatures and is less irritating to the skin and eyes. Iodine is used in emergency water disinfection situations and for smaller volumes of water, such as in portable water purification systems.

Thus, while chlorine, bromine, and iodine serve crucial roles in disinfecting water to ensure its safety for human consumption, fluorine is not utilized for disinfection but rather for health benefits related to dental hygiene.