Which of the following best describes how to calculate the average atomic mass of an element?

• A. Add the masses of all isotopes and divide by the number of isotopes.
• B. Multiply the mass of each isotope by its natural abundance (as a decimal), then sum these values for all isotopes.
• C. Use only the mass of the most abundant isotope as the atomic mass.
• D. Subtract the mass of the least abundant isotope from the mass of the most abundant isotope.

Answer: (B)

Verified step by step guidance

1. Understand that the average atomic mass of an element is a weighted average of the masses of its naturally occurring isotopes, reflecting their relative abundances.
2. Identify the mass of each isotope of the element and its corresponding natural abundance, which is usually given as a percentage.
3. Convert the natural abundance percentages into decimal form by dividing each percentage by 100.
4. Multiply the mass of each isotope by its decimal abundance to find the weighted contribution of each isotope to the average atomic mass.
5. Sum all the weighted contributions from each isotope to obtain the average atomic mass of the element.