Which of the following would not be used as a coagulant?

The correct choice for this question is based on the role and function of coagulants in water treatment processes. Coagulants are chemicals that promote the aggregation of fine particles in water, thereby helping to remove solids and improve water clarity.

Black alum, ferric chloride, and chlorinated copperas are all effective coagulants. Black alum, which is a specific type of aluminum sulfate, aids in the coagulation process by neutralizing the charges on particles, allowing them to clump together and settle out of the water. Ferric chloride functions similarly, providing an iron source that forms flocs when interacting with suspended particles, facilitating their removal. Chlorinated copperas, or ferrous sulfate, can also serve as a coagulant by forming insoluble particles that trap impurities as they settle.

Sodium hypochlorite, on the other hand, is primarily used as a disinfectant and oxidizer rather than a coagulant. It is effective at killing bacteria and other pathogens in water but does not have the coagulating properties necessary for the removal of suspended solids. Therefore, it would not be utilized in the coagulation process, making it the correct choice for this question.