The correct answer is protons. Explanation & Key Takeaways: • The atomic number of an element is the same as the number of protons. • The number of electrons = number of protons. • Hence, the total number of electrons present in an atom represents the atomic number of a particular atom. • Elements are different because of their atomic number. • The periodic table displays all of the known elements and is arranged in order of increasing atomic number. Related Concepts: • Neutrons are subatomic particles that are one of the primary constituents of atomic nuclei. • Atoms of a chemical element that differ only in neutron number are called isotopes. • Neutron was discovered by James Chadwick in 1932. • An electron is a negatively charged subatomic particle that together with protons and neutrons form an atom's nucleus. • Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism, chemistry and thermal conductivity, and they also participate in gravitational, electromagnetic and weak interactions. • Electron was discovered by J J Thomson. • Protons are the positively charged particles which are present in the nucleus of an atom. • They provide the attractive electrostatic central force which binds the atomic electrons. • It was observed as H^(+) by Eugen Goldstein (1886). It was identified in other nuclei (and named) by Ernest Rutherford (1917–1920).