Which substance can be used to detect chlorine leaks around a chlorine cylinder?

Ammonia is used to detect chlorine leaks around a chlorine cylinder due to its specific chemical reaction with chlorine gas. When ammonia comes into contact with chlorine, it produces a white cloud of ammonium chloride. This distinct visual cue is a clear indicator that chlorine is present in the area, allowing operators to recognize the leak and take appropriate safety measures.

Using water would not be effective in detecting chlorine leaks because it does not react with chlorine gas in a way that provides visible evidence of the leak. Chlorine itself is not a practical detector since it would pose a health risk and would not indicate the leak's location effectively. Hydrogen peroxide also does not provide a reliable means of detecting chlorine gas in the same way that ammonia does. Therefore, ammonia is the most suitable option for this purpose due to the immediate and visible reaction it produces.