What is commonly used to locate chlorine leaks?

The most appropriate answer is ammonia. Ammonia is commonly used to detect chlorine leaks because it reacts with chlorine to produce chloramines. When a chlorine leak occurs, the presence of ammonia in the area will lead to the formation of chloramines, which can be detected by their characteristic odor. This method is effective for identifying leaks in systems where chlorine is being used as a disinfectant, particularly because chloramines can serve as an indicator of chlorine levels and the potential leaks present.

The other options are not utilized as leak detection agents in the same way. Chloramines, while they are formed from the reaction between chlorine and ammonia, are not a separate detection method; rather, they are a result of the reaction. Hypochlorous acid is a form of chlorine that is present in water and does not play a role in leak detection. Trihalomethanes are byproducts of chlorination and are not used to locate leaks, but rather to identify potential water quality issues.