Hmm … not sure … I think its hydrogen, the simplest of the elements (just one proton) and the starting material for lots of stars. The gas condenses to form stars; the nuclear fusion reactions convert hydrogen to heavier atoms; so, despite the fact that our sun has been burning for a while it still has quite a lot of hydrogen, as you can see at:
I would think it would have to be Hydrogen. Hydrogen is the most abundant element in the whole universe and something like 90% of all the atoms in the universe are hydrogen atoms. That sounds pretty common to me!