What is the average mass assigned to one atom of a naturally occurring element?

• A. Formula Mass
• B. Atomic Mass
• C. Law of Definite Composition
• D. Jet Streams

Answer: (B)

Atomic mass is the average mass assigned to one atom of a naturally occurring element. It represents the weighted average of the masses of all the element’s isotopes as they occur in nature, expressed in atomic mass units. That’s why the periodic table shows a non-integer value for many elements—the atomic mass reflects the relative abundances of different isotopes.

Formula mass sums the masses of atoms in a specific chemical formula (useful for compounds, not a single atom), and the Law of Definite Proportions describes fixed ratios in compounds rather than the mass of individual atoms. Jet streams are unrelated to atomic structure. So the concept described here is atomic mass.