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

• A. Yes, if they have the same number of protons but different numbers of neutrons.
• B. Yes, if they have the same mass number but different atomic numbers.
• C. No, isotopes must have the same atomic number and mass number.
• D. No, isotopes must have 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 atomic number defines the element, so isotopes must have the same atomic number but can differ in mass number due to varying neutrons.
3. Analyze the question: can two atoms with the same mass number be isotopes? Since isotopes differ in neutron number, having the same mass number means the total number of protons plus neutrons is the same.
4. If two atoms have the same mass number but different atomic numbers, they must have different numbers of protons and neutrons, meaning they are different elements (isobars), not isotopes.
5. Therefore, two atoms with the same mass number cannot be isotopes because isotopes require the same atomic number but different mass numbers.