Which of the following may indicate the presence of a chlorine leak when ammonia is sprayed in the air?

The presence of a white cloud when ammonia is sprayed in the air can indicate a chlorine leak due to the formation of ammonium chloride. When chlorine gas comes into contact with ammonia, a chemical reaction occurs, resulting in a visible white cloud, which consists of particulate ammonium chloride. This reaction is significant in water treatment processes where chlorine is used as a disinfectant, and ammonia is sometimes added to stabilize chlorine levels.

Other indicators, while potentially suggestive of different conditions, do not specifically indicate a chlorine leak in this context. For instance, a greenish mist is typically associated with chlorine gas itself, not the reaction between chlorine and ammonia. An audible hiss might suggest a gas leak, but it does not indicate the specific chemical interactions taking place. A temperature drop can occur in various chemical reactions but is not a reliable indicator of chlorine presence or leakage compared to the visual cue of a white cloud.