HCl

Hydrochloric acid may be found as a liquid and a vapour.

NOTE: When sampling the odours of unknown chemicals it is a good idea to use your hand to gently waft the vapour to your nose, rather than taking a big ol' snort. This is particualrly true if the unknown sample is actually 6M HCl.

Alternately, you may remove HCl vapour from a contaminated air stream with activated carbon impregnated with potassium hydroxide.

This is one of the six strong acids. It's chemical formula is HCl. That's one atom of hydrogen, and one atom of chlorine. Hydrochloric acid, like all acids, is a molecule. Like only the strong acids though, it dissociates 100% in water to form hydronium ions and chloride ions.