Harmful solidliquid and gases

Solids, I say lead is pretty harmful. So is Uranium (whether it's liquid or solid).

Liquids, I pretty sure Mercury is one of the worst, if you touch it, it disolves into your skin. (Which is bad) Gasoline is also pretty bad along with oil.

Gases, I say Methane (A big cause in global warming), and Helium if you breathe too much, and Radium (Radiation), as well as flammable hydrogen.