Three of the groups below hold only substances that are gases in an ordinary room. Choose the group that breaks the classification.

Oxygen, nitrogen, helium, argon, neon, krypton, ozone, ammonia and chlorine are all gases at room temperature, and so are hydrogen and methane. Bromine, though, is a deep red liquid at room temperature — the only other element that is liquid then is mercury — so the group holding bromine is the one that breaks the rule.