The nucleus of an atom consists of protons and neutrons. These two particles are found in the center of an atom, and they are responsible for determining the chemical properties of an element.
Protons are positively charged particles, and neutrons are neutral particles that have no charge. Together, these particles make up the nucleus of an atom, which is usually much smaller than the overall size of the atom.
The number of protons in an atom is called the atomic number, and it determines what element the atom is. For example, all hydrogen atoms have one proton in their nucleus, and all helium atoms have two protons.