Which of the following is the same among isotopes of the same element?

• A. Number of neutrons
• B. Number of protons
• C. Mass number
• D. Atomic mass

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 different numbers of neutrons.
2. Understand that the number of protons defines the element and is called the atomic number.
3. Recognize that the number of neutrons can vary among isotopes, which changes the mass number (sum of protons and neutrons).
4. Note that atomic mass is the weighted average mass of all isotopes of an element, so it can differ among isotopes.
5. Therefore, the property that remains the same among isotopes of the same element is the number of protons.