What does the atomic number of an element signify?

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 property uniquely identifies an element, as different elements have different numbers of protons. For instance, hydrogen, which has an atomic number of 1, has one proton, while carbon has an atomic number of 6, indicating that it contains six protons.

In a neutral atom, the number of protons also equals the number of electrons, which determines the atom's overall charge. However, since the question specifically asks about the atomic number, it is important to highlight that it primarily pertains to protons.

The other potential answers do not accurately describe the atomic number. For instance, the total number of neutrons is not related to the atomic number but is indicated by the mass number, which is the sum of protons and neutrons. The number of electrons in ionized atoms can vary depending on the ion's charge, making it an unreliable indicator of atomic number in general. Finally, the average mass of an atom refers to the atomic mass, which is a weighted average based on isotopes and their relative abundances, rather than directly correlating to the number of protons. Thus, the atomic number