The hazard symbol for chlorine gas is a green cylinder with a white cross. This symbol represents corrosive materials, which is a category that chlorine gas falls under.

Here's why:

* Corrosive: Chlorine gas is highly corrosive, meaning it can damage tissues and materials upon contact.

* Toxic: It is also a highly toxic gas that can cause respiratory issues and even death at high concentrations.

It's important to remember that this symbol is just one aspect of hazard communication. Always consult the Safety Data Sheet (SDS) for chlorine gas for complete information on its hazards and proper handling procedures.