Isotopes are atoms of the same element that differ in the number of what?

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

Answer: (A)

Isotopes are atoms of the same element that differ in the number of neutrons in the nucleus. The identity of an element is set by how many protons it has, so isotopes share the same proton count. Changing neutrons alters the atomic mass and some nuclear properties without changing the element’s chemical behavior. Electrons determine charge and bonding, but isotopes can have the same or different electron counts depending on ionization, and orbitals are just the electron energy levels, not what distinguishes different isotopes. So the differing component that creates isotopes is the number of neutrons.