For future reference, fusion happens in stars (and at the center of supernovas). H combining with O2 is a chemical reaction rather than a nuclear reaction. On

For future reference, fusion happens in stars (and at the center of supernovas). H combining with O2 is a chemical reaction rather than a nuclear reaction. On the other hand, the question regarding how supernovas combine/mix heavy atoms to form chemicals would be a very interesting PhD thesis. :D