The correct answer is a) proton.
Protons are subatomic particles found in the nucleus of an atom, and they carry a positive electric charge. Each proton has a charge of +1. This positive charge is crucial for the stability of atoms, as it helps to attract negatively charged electrons, which orbit around the nucleus. In contrast, neutrons (option b) are neutral particles, meaning they have no charge, and electrons (option c) carry a negative charge. Understanding these charges is fundamental to the study of atomic structure and chemistry.