Political Elements
Innofensium Pc
Precisely equal numbers of electrons, protons, neutrons, leptons, quarks. Completely inert, utterly useless, but smells like a rose.
Budweisium Ps
Has no taste or smell; is often indistinguishable from water.
Politicium Po
Contains a great deal of gas. Similar to radon in that it can reach lethal concentrations in the House of Commons.
Commons Cm
Atomic number 600 (approx.). Can never be found in a solution.
With thanks to JayDee's joke page.