The quantity of protons in an element is identified by its what?

The quantity of protons in an element is identified by its atomic number. The atomic number is a fundamental characteristic of an element and directly reflects the number of protons found in the nucleus of each atom of that element. This number also determines the element's identity; for example, hydrogen has an atomic number of 1, meaning it has one proton, while oxygen has an atomic number of 8, indicating it has eight protons.

In contrast, the mass number refers to the total number of protons and neutrons in an atom's nucleus, which means it does not exclusively identify protons. Atomic weight is a measure of the average mass of atoms of an element, accounting for the presence of isotopes and their relative abundances. A molecular formula, on the other hand, describes the composition of a molecule in terms of the different elements it contains and cannot specifically indicate the number of protons in an element. Thus, the atomic number is the correct interpretation for identifying the quantity of protons in an element.