What does relative mass indicate for an atom?

Relative mass for an atom refers to how heavy it is compared to another atom, using a standard model, usually based on carbon-12, which is assigned a relative mass of 12 units. This concept allows scientists to understand the mass of different elements in relation to one another rather than providing absolute mass values, which can vary greatly given different units of measurement.

This comparison is crucial in chemistry as it facilitates stoichiometric calculations and the understanding of chemical reactions, where the mass of reactants and products is significant. By using a standard isotope like carbon-12 as a reference point, scientists can communicate effectively regarding the mass of elements and compounds in a consistent manner.

Other options pertain to specific properties of atoms: the total number of protons corresponds to the atomic number, the total number of neutrons is a separate calculation that can vary even among isotopes of the same element, and neither of those quantifies the relative mass in the context of how one atom's mass compares to another.