The atomic number equals the number of what?

• A. Protons
• B. Neutrons
• C. Electrons
• D. Quarks

Answer: (A)

The atomic number is the count of protons in the nucleus. This number defines the identity of the element on the periodic table—each element has a unique number of protons. Neutrons contribute to the mass but not to the element’s identity, so they don’t set the atomic number. Electrons are equal to protons only in a neutral atom, balancing charge, but the atomic number itself is specifically the proton count. Quarks are constituents inside protons and neutrons, not what determines the atomic number. For example, carbon has six protons, so its atomic number is six.