Which term describes the mass of a single atom relative to the mass of carbon-12?

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

Answer: (A)

The mass of a single atom relative to carbon-12 is described as its atomic mass, and it's measured in atomic mass units (amu). Carbon-12 is defined to be exactly 12 amu, so the atomic mass tells you how heavy that atom is on the amu scale. For example, hydrogen is about 1.008 amu and carbon is about 12.01 amu. Sometimes people use the term relative atomic mass (Ar) to describe this same idea as a dimensionless ratio to carbon-12, but when talking about the mass of a single atom in the standard unit, atomic mass in amu is the right concept. The other terms don’t fit: formula mass applies to molecules, the law of definite composition is a principle about compound composition, and jet streams aren’t related to atomic masses.