The atomic number of an atom is equivalent to the number of: electrons protons neutrons alpha particles protons and neutrons

The correct answer is:<br /><br />**protons**<br /><br />### Explanation:<br />The atomic number of an atom is defined as the number of **protons** in the nucleus of an atom. It uniquely identifies a chemical element and determines its position on the periodic table. <br /><br />- **Electrons**: In a neutral atom, the number of electrons equals the number of protons, but the atomic number specifically refers to protons.<br />- **Neutrons**: The number of neutrons can vary in isotopes of the same element, so it does not define the atomic number.<br />- **Alpha particles**: These are helium nuclei (2 protons and 2 neutrons) and are unrelated to the atomic number.<br />- **Protons and neutrons**: Together, they make up the mass number, not the atomic number.<br /><br />Thus, the atomic number is equivalent to the number of **protons**.