Where were most of the elements "forged" on the periodic table

Answer: Stars

Most of the chemical elements of the Periodic Table were formed or "forged" in the different types of stars that exists in the universe in their different phases of life.

For example, a young star is composed mainly of Hydrogen, the simplest chemical substance and the first in the Periodic Table; being this the element that leads to the other known elements. Taking into account that the two components of each hydrogen atom (1 proton and 1 electron) are separated, the great pressure within the star manages to merge (fuse) two protons.

What does this mean?

Well, sometimes a proton captures an electron and becomes a neutron, but when two protons and two neutrons join together, they form the Helium nucleus, which is the second element in the periodic table. Then, when two helium nuclei join and form the nucleus of another element, Beryllium and so on.

So, by means of the nuclear fusion process the nuclei of most of the elements lighter than Iron (which is the chemical element 26 of the periodic table) can be formed.

Now, elements that are heavier than Iron can be forged within the stars through the capture of neutrons. In this way, the collapse of the star's center core occurs so quickly that it generates huge shock waves that eject the outer layers of the star into space becoming a supernova. Then, it is during the few seconds of collapse that the specific pressure and temperature conditions in the supernova are created and allow heavier elements to be generated and expelled as interstellar dust and gas.

In this sense, with the explosion of more massive stars and white dwarfs other chemical elements are formed, as well as others that are formed by dying stars of low mass and neutron stars.

However, it should be noted that there are also chemical elements that are artificially formed in experimental fusion nuclear reactors.