Which of the following statements about atomic weight is true?

• A. Atomic weight is always equal to the mass number of the most abundant isotope.
• B. Atomic weight is the weighted average mass of all naturally occurring isotopes of an element.
• C. Atomic weight is the same as the atomic number of an element.
• D. Atomic weight is measured in units of grams per mole.

Answer: (B)

Verified step by step guidance

1. Understand that atomic weight (also called atomic mass) represents the average mass of all naturally occurring isotopes of an element, weighted by their relative abundances.
2. Recall that the mass number is the total number of protons and neutrons in a single isotope, which is a whole number and specific to that isotope, not an average.
3. Recognize that atomic number is the number of protons in an element and does not relate to atomic weight directly.
4. Note that atomic weight is a dimensionless quantity (often expressed in atomic mass units, amu) and is not measured in grams per mole; grams per mole is the unit for molar mass.
5. Conclude that the true statement is: Atomic weight is the weighted average mass of all naturally occurring isotopes of an element.