What method can be used to detect chlorine leaks around chlorine cylinders?

The detection of chlorine leaks around chlorine cylinders is most effectively accomplished using ammonia. When ammonia comes into contact with chlorine gas, it produces a noticeable white smoke or cloud, which is an immediate indicator of a leak. This reaction occurs because chlorine is a strong oxidizer and reacts readily with ammonia, making it a practical and visual way to identify the presence of chlorine gas in the environment.

In contrast, the other substances listed do not serve as effective or safe methods for chlorine leak detection. Carbon dioxide, hydrochloric acid, and oxygen do not react with chlorine in a manner that would create a visible indication like the white smoke generated by the interaction with ammonia. Consequently, using ammonia provides a straightforward and efficient means of identifying potential chlorine leaks, ensuring timely response measures can be taken to ensure safety.