Two atoms have the same number of protons but different numbers of neutrons. What can you conclude about these two atoms?
That they are isotopes, i.e. the same element, but different atomic masses.
The number of nuclear protons gives
Of course while there may be the same number of nuclear protons, the nucleus may contain different numbers of neutrons; these give rise to different isotopes; same element, and same chemistry, but different atomic mass. Most elements have a number of isotopes. The quoted atomic mass that appear on the Periodic Table are the weighted average of the isotopes.