How is the relative atomic mass calculated?

The relative atomic mass is calculated using the weighted average of the masses of an element's isotopes, taking into account their natural abundances. The correct method involves multiplying the mass of each isotope by its relative abundance, summing these values, and then dividing by the total abundance of the isotopes. This gives a precise measure of the average mass of an atom of the element, reflecting the contribution of each isotope proportionally to how common it occurs in nature.

This approach is crucial because different isotopes of an element can have significantly different masses due to variations in the number of neutrons, and their abundance impacts the average value used on the periodic table. This method ensures that the resulting relative atomic mass is representative of the element as it is found in nature.