What disinfectant is typically formed when ammonia is added to chlorine for treating drinking water?

When ammonia is introduced to chlorine in the process of treating drinking water, chloramines are formed. This reaction occurs when chlorine interacts with ammonia, producing various forms of chloramine, primarily monochloramine, which is widely used for disinfection in public water systems. Chloramines are particularly valued in water treatment because they provide a more stable and longer-lasting residual disinfection effect in the water distribution system compared to free chlorine alone. This is important for maintaining water quality along longer pipelines and helps in preventing the regrowth of bacteria.

Sodium hypochlorite is a compound often used as a disinfectant, but it does not form from the reaction between ammonia and chlorine; rather, it is a product of chlorine being dissolved in water. Hypochlorous acid is a weak acid that forms when chlorine is dissolved in water, but again, it is not formed by the direct interaction with ammonia. Trihalomethanes are a group of chemical compounds that can form as byproducts during the disinfection of water, particularly when chlorine reacts with organic matter, and are not related to the reaction of ammonia and chlorine. Thus, the formation of chloramines is the key reaction that occurs when ammonia is added to chlorine, making it the correct answer.