Which term refers to the relative atomic mass of an atom on a scale where carbon-12 is 12 units?

The term that refers to the relative atomic mass of an atom on a scale where carbon-12 is defined as having a mass of 12 units is relative atomic mass. This measurement provides a comparison of the mass of an atom of a specific element to the mass of a carbon-12 atom. The relative atomic mass is a dimensionless quantity, as it is a ratio of masses, which simplifies comparisons between different elements.

In contrast, relative molecular mass pertains to the mass of a molecule compared to carbon-12, which is not relevant in this context since the question specifically addresses individual atoms. Molar volume refers to the volume occupied by one mole of a substance, usually in a gas at standard temperature and pressure, and is unrelated to atomic mass. Mass number, on the other hand, is the total number of protons and neutrons in an atomic nucleus, and while it provides information about the composition of the nucleus, it does not represent the mass comparison relative to carbon-12. Thus, the most accurate term for this context is relative atomic mass.