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

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

Answer: (C)

Verified step by step guidance

1. Understand that the average atomic mass of an element is a weighted average based on the masses and relative abundances of its isotopes.
2. Identify the mass of each isotope of the element and its corresponding natural abundance (usually given as a percentage).
3. Convert the percentage abundance of each isotope into a decimal by dividing 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 using the formula: \(\text{Average Atomic Mass} = \sum (\text{mass of isotope} \times \text{fractional abundance})\).