What does mass number represent in an atom?

The mass number of an atom specifically represents the total count of protons and neutrons present in its nucleus. Protons are positively charged particles, and neutrons have no charge, while electrons, which are negatively charged, do not contribute to the mass number because their mass is negligible compared to that of protons and neutrons. Thus, mass number provides a direct indication of the mass and stability of an atom, as it combines the contributions from the two most significant particles in the nucleus. Understanding mass number is essential for grasping concepts in atomic structure, isotopes, and nuclear reactions, as it reflects the identity of an element and its isotopes.