Atomic Number, as defined in the material, is the total number of what?

• A. Protons
• B. Neutrons
• C. Electrons
• D. Protons and neutrons

Answer: (D)

Atomic number is the number of protons in the nucleus. This fixed count defines the identity of an element and determines its position in the periodic table. Neutrons contribute to the mass but not to the charge, so they don’t change the atomic number. Electrons can vary in charged species, so counting them wouldn’t reliably identify the element. The sum of protons and neutrons is the mass number, not the atomic number.