What is the hazard symbol for chlorine gas?
it is corrosive
You'd still have poisonous chlorine gas, and it would be as toxic as it was before you added the neutron. But there is more news, and it's bad. By adding a neutron to each of the atoms, you'd end up with unstable isotopes of chlorine, which means that all your chlorine gas is now radioactive and presents a radiation hazard as well as being as poisonous as it was originally.