Protons are subatomic particles that carry a positive electric charge and are located in the nucleus of an atom. For an atom of magnesium (Mg), protons determine the element’s atomic number (12), which identifies it uniquely. The number of protons in an Mg nucleus directly affects the atom’s overall charge and contributes to the formation of different isotopes of Mg with varying numbers of neutrons. Understanding the properties of protons is crucial for comprehending the structure of matter, as they play a central role in determining an element’s identity and behavior.