Thorium occurs quite widely in nature, the best source is monazite sand. Extraction is a chemical process, see the Wikipedia article on Thorium
Radon gas is the radioactive gas produced from uranium and thorium. It forms from the radioactive decay of small amounts of uranium and thorium naturally present in rocks and soils so some radon...
Isotopes of radon (Rn)
hydrogen
Tiger electronics
No, the impact energy of a meteor is all from kinetic energy, nothing nuclear is involved.