Which of the following compounds is considered a disinfection by-product?

Trihalomethanes (THMs) are indeed considered disinfection by-products formed during the chlorination process of drinking water. When chlorine interacts with organic matter present in the water, it can create these unwanted by-products, which can have health implications if consumed in high concentrations over time. THMs are a key concern in water treatment because they are identifiable compounds that can accumulate, and their formation is a direct consequence of the disinfection process aiming to kill pathogens.

Chlorine itself is widely used as a primary disinfectant but is not classified as a disinfection by-product; rather, it is an agent meant to eliminate harmful microorganisms. Ozone is another strong disinfectant used in water treatment that, while capable of forming disinfection by-products under certain circumstances, does not fall into the category of the by-products itself. Ammonia is often used in combination with chlorine to help control and optimize disinfection processes but is not a product formed as a result of disinfection. Thus, THMs stand out as specific compounds produced during water disinfection processes that can pose risks if not monitored properly.