Which term refers to the average mass of all the naturally occurring isotopes of an element?

• A. Atomic number
• B. Molar mass
• C. Mass number
• D. Atomic mass

Answer: (D)

Verified step by step guidance

1. Understand that elements can have multiple isotopes, which are atoms with the same number of protons but different numbers of neutrons.
2. Recognize that the term 'atomic number' refers to the number of protons in an atom and does not account for isotopes.
3. Know that 'mass number' is the total number of protons and neutrons in a specific isotope, not an average over isotopes.
4. Understand that 'molar mass' refers to the mass of one mole of a substance, usually expressed in grams per mole, and is related but not the same as the average atomic mass.
5. Identify that 'atomic mass' (also called atomic weight) is the weighted average mass of all naturally occurring isotopes of an element, taking into account their relative abundances.