Which number represents protons in an element?

The atomic number of an element is defined as the number of protons present in the nucleus of an atom of that element. This fundamental characteristic distinguishes one element from another; for example, hydrogen, which has an atomic number of 1, has one proton, while carbon, with an atomic number of 6, has six protons. The atomic number is critical not just for identification but also plays a role in determining the element's chemical properties.

In contrast, the mass number refers to the total number of protons and neutrons in an atom's nucleus and does not provide direct information about the number of protons alone. The charge number typically refers to the total charge of the atom based on the balance of protons and electrons, while the neutron number indicates how many neutrons are present in the nucleus, which does not affect the identification of the element itself. Therefore, the atomic number is the correct answer as it accurately describes the quantity of protons in an element, establishing its identity in the periodic table.