What determines the identity of an element?

• A. The number of neutrons
• B. The atomic mass
• C. The number of protons
• D. The number of electrons

Answer: (C)

The element’s identity comes from how many protons are in the nucleus. That number, called the atomic number, uniquely labels the element and sets its place on the periodic table. Neutrons can vary, producing different isotopes with different masses, but as long as the proton count is the same, you’re talking about the same element. The atomic mass grows with the number of neutrons, so it’s not the defining feature of the element. Electrons can be gained or lost, creating ions, which changes charge and chemical behavior but not the element’s identity, since the identity is anchored in the nucleus. If you were to change the number of protons, you would get a different element altogether with a different set of properties.