Which chemical is used in breakpoint chlorination to ensure water is safe for consumption?

The correct choice is chlorine, which is essential in the process of breakpoint chlorination. This method involves adding chlorine to water until a point is reached where all the chlorine combines with contaminants (such as ammonia) in a reaction known as chlorination. Beyond this breakpoint, additional chlorine is added, resulting in a free chlorine residual that is effective in disinfecting the water.

Breakpoint chlorination ensures that any harmful microorganisms present in the water are effectively killed, making the water safe for consumption. This process is crucial in ensuring adequate levels of disinfection, particularly in surface water sources where contamination is more likely.

Other options, such as fluoride, sodium bicarbonate, and magnesium sulfate, do not play a role in the disinfection process in the same way that chlorine does. Fluoride is typically used for dental health, sodium bicarbonate can be used to adjust pH levels, and magnesium sulfate may serve as a coagulant in water treatment processes, but none of these substances are used to ensure the safety of drinking water through the disinfection method provided by breakpoint chlorination.