What term refers to the number of protons in the nucleus of an atom?

The term that refers to the number of protons in the nucleus of an atom is known as the atomic number. This fundamental property of an element determines its identity and position in the periodic table. The atomic number not only signifies the number of protons but also indicates the number of electrons in a neutral atom, which ultimately influences the atom's chemical behavior.

In contrast, atomic mass refers to the weighted average mass of an atom's isotopes, taking into consideration both protons and neutrons. The molecular number is not a standard term in chemistry; it often causes confusion with molecular weight, which is the sum of the atomic masses of all atoms in a molecule. Elemental charge pertains to the overall charge of an atom or ion, influenced by the number of protons and electrons but does not specifically indicate the total number of protons. Thus, the precise definition and significance of atomic number make it the correct choice.