Which property of isotopes of the same element must be different?

• A. Number of protons
• B. Number of neutrons
• C. Atomic number
• D. Chemical symbol

Answer: (B)

Verified step by step guidance

1. Recall that isotopes are atoms of the same element that have the same number of protons but differ in the number of neutrons.
2. Understand that the number of protons defines the atomic number and the identity of the element, so it remains constant for isotopes.
3. Recognize that the chemical symbol is based on the element's identity, which depends on the number of protons, so it also remains the same for isotopes.
4. Therefore, the property that must be different among isotopes is the number of neutrons, which affects the atomic mass but not the chemical behavior significantly.
5. Summarize that isotopes have the same atomic number (number of protons) but different neutron counts, leading to different mass numbers.