Alchemy was a form of speculative thought that, among other aims, tried to transform base metals such as lead or copper into silver or gold. It also sought to discover cures for diseases and a way of extending life.
Today we know that the universe is made up of atoms and elements. Since lead and other metals are not composed of fire, air, earth, and water, it's not possible to adjust the percentages of those elements and turn them into gold.
(Unfortunately, it turns out that alchemy, at least in its purest form, can’t be done. You can’t turn any metal into gold, no matter how much sorcery or chemicals or mystical charms you use. )
I hope I helped