Isotopes of the same element differ primarily in which property?

Isotopes of the same element differ primarily in which property?

• A. Number of protons
• B. Number of neutrons
• C. Number of electrons
• D. Mass number

Answer: (B)

Isotopes share the same number of protons, which fixes the element’s identity and most of its chemical behavior. They differ in the number of neutrons, which changes the mass of the nucleus without altering the chemical properties much. Since mass number equals protons plus neutrons, varying the neutron count makes isotopes have different mass numbers. The number of electrons typically matches the number of protons in neutral atoms, so it doesn’t drive the isotope difference. So the property that changes the most among isotopes is the number of neutrons.

Isotopes share the same number of protons, which fixes the element’s identity and most of its chemical behavior. They differ in the number of neutrons, which changes the mass of the nucleus without altering the chemical properties much. Since mass number equals protons plus neutrons, varying the neutron count makes isotopes have different mass numbers. The number of electrons typically matches the number of protons in neutral atoms, so it doesn’t drive the isotope difference. So the property that changes the most among isotopes is the number of neutrons.