Proton

A proton is a tiny, positively charged particle found in the nucleus at the center of every atom, and it's one of the basic building blocks of all matter in the universe. Protons are incredibly small but surprisingly heavy for their size, and the number of protons in an atom's nucleus determines what chemical element it is, so every hydrogen atom has one proton while every gold atom has 79. Think of protons as fundamental "identity cards" for atoms—they define what substance you're actually looking at.