Can two atoms with the same mass number ever be isotopes of each other?

• A. Yes, any two atoms with the same mass number are always isotopes.
• B. No, if two atoms have the same mass number but different atomic numbers, they are not isotopes but isobars.
• C. Yes, if they have the same atomic number but different numbers of neutrons.
• D. No, isotopes must have the same atomic number but different mass numbers.

Answer: (B)

Verified step by step guidance

1. Recall the definition of isotopes: isotopes are atoms of the same element that have the same atomic number (number of protons) but different numbers of neutrons, resulting in different mass numbers.
2. Understand that the mass number (A) is the sum of protons (Z) and neutrons (N), so \(A = Z + N\).
3. If two atoms have the same mass number but different atomic numbers, they have different numbers of protons and neutrons arranged differently; such atoms are called isobars, not isotopes.
4. Therefore, isotopes must have the same atomic number but different mass numbers, meaning they differ in neutron count but belong to the same element.
5. Conclude that two atoms with the same mass number cannot be isotopes if their atomic numbers differ; they are isobars instead.