Which property is shared by all isotopes of calcium, and which property differs among them?

• A. All have the same mass number; they differ in the number of electrons.
• B. All have the same number of electrons; they differ in the number of protons.
• C. All have the same number of neutrons; they differ in the number of protons.
• D. All have the same number of protons; they differ in the number of neutrons.

Answer: (D)

Verified step by step guidance

1. Recall that isotopes of an element have the same number of protons but differ in the number of neutrons. The number of protons defines the element itself.
2. Understand that the number of protons in the nucleus is called the atomic number, which is constant for all isotopes of a given element (in this case, calcium).
3. Recognize that the mass number of an isotope is the sum of protons and neutrons, so different isotopes have different mass numbers due to varying neutron counts.
4. Note that the number of electrons in a neutral atom equals the number of protons, so isotopes of calcium also have the same number of electrons if they are neutral.
5. Therefore, the shared property among all calcium isotopes is the number of protons, and the differing property is the number of neutrons.