Question

What elements are made when a star forms?

Answer 1

ALL the natural periodic elements are formed in the stars nucleus, indeed. But the kind of the element depends on what stage of its "life" the star reached.

Explanation:

Stars are massive astronomical bodies of matter constituted mainly by Hidrogen gas (`H2`), the simplest and most abundant matter spread all over the universe.

At very high pressure and temperature in the nucleus of a star, caused by the imense gravity of a very dense matter collapsing on itself, Hidrogen could be severely transformed in Helium (`He`) by means of a nuclear reaction, called nuclear fusion. The nuclear fusion is a physical reaction and consists on the fusion of atomic nuclei of two atoms, forming only one atom in the end of the process and thus liberating a massive amount of energy. This energy could trigger other processes of fusion, getting more and more "complex" to form a gradual scale of all the other chemical species of atoms, starting from Hidrogen and thus ending with the most "heavy" known natural atoms.

The most powerful reaction in the universe is called Supernova, which means that a dying star explodes forming by complexes nuclear reactions the heavier periodic elements.

Progressively, and as a consequence of the natural consumption of Hidrogen by its nuclear fusion, we could even determine how old a star is and in what evolutionary stage it's set because of its "chemical signature", in other words: the more Hidrogen it contains proportionally to other elements, the younger the star is.