Isotopes are atoms of the same element that have different numbers of neutrons.

• A. False
• B. True
• C. They have different numbers of protons
• D. They have different numbers of electrons

Answer: (B)

Isotopes are defined by having the same number of protons but different numbers of neutrons. Since protons determine which element an atom is, isotopes stay the same element even as their neutron count changes. Changing neutrons changes the mass of the atom, but not its identity. For example, carbon-12 and carbon-14 both have six protons, but carbon-12 has six neutrons and carbon-14 has eight neutrons, giving different mass numbers. Chemically, they behave similarly because chemistry is driven mainly by electrons, which equal the number of protons in a neutral atom. The difference in neutrons mainly affects physical properties and stability; some isotopes are radioactive. The other statements would imply a different element (different protons) or a charged species (different electrons), which is not what defines isotopes.