Which of the following is a coagulant used in water treatment?

Alum, chemically known as aluminum sulfate, is widely recognized as a coagulant used in water treatment processes. Its primary function is to help remove suspended solids from water. When added to water, alum reacts with the impurities, causing them to clump together into larger particles, known as flocs, which can then be more easily removed through sedimentation or filtration. This process is crucial for the clarification of drinking water and reducing turbidity.

In contrast, chlorine is primarily used as a disinfectant to kill pathogens in water rather than as a coagulant. Fluoride is added to promote dental health, and bromine is sometimes used for disinfection but does not serve as a coagulant. Each of these substances plays a distinct role in water treatment, with alum specifically focused on improving the physical characteristics of water through coagulation.