The average atomic mass of aluminum is 26.98 amu. Which statement is true about the mass of individual aluminum atoms?

• A. All aluminum atoms have a mass less than 26.98 amu.
• B. The mass of individual aluminum atoms can vary, but the average is 26.98 amu.
• C. No aluminum atom has a mass greater than 26.98 amu.
• D. Most aluminum atoms have a mass exactly equal to 26.98 amu.

Answer: (B)

Verified step by step guidance

1. Understand that the average atomic mass of an element, such as aluminum, is a weighted average of the masses of all its naturally occurring isotopes.
2. Recognize that individual atoms of aluminum can have different masses because they may be different isotopes, which have the same number of protons but different numbers of neutrons.
3. Recall that the average atomic mass (26.98 amu for aluminum) is not the mass of any single atom but a calculated average based on the relative abundance and mass of each isotope.
4. Conclude that some aluminum atoms have masses less than 26.98 amu, some have masses greater than 26.98 amu, and the average reflects the overall distribution.
5. Therefore, the correct statement is that the mass of individual aluminum atoms can vary, but the average is 26.98 amu.