In the isotope polonium-218, what does the number 218 represent?

• A. The atomic number, which is the number of protons in the nucleus
• B. The number of electrons in a neutral atom
• C. The number of neutrons in the nucleus
• D. The mass number, which is the sum of protons and neutrons in the nucleus

Answer: (D)

Verified step by step guidance

1. Understand that isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
2. Recall that the atomic number represents the number of protons in the nucleus and defines the element.
3. Know that the mass number is the sum of protons and neutrons in the nucleus of an atom.
4. Recognize that in the notation polonium-218, the number 218 refers to the mass number, not the atomic number or number of neutrons alone.
5. Therefore, the number 218 represents the total number of protons and neutrons in the nucleus of polonium-218.