No, every atom of an element does not necessarily have the same number of nucleons.
Nucleons refer to the particles found in the nucleus of an atom, which includes protons and neutrons. The sum of the protons and neutrons in an atom gives the mass number of that atom.
Within an element, different atoms can have different numbers of neutrons, resulting in different isotopes of the same element. Isotopes are atoms of the same element that have the same number of protons (hence the same atomic number) but different numbers of neutrons (resulting in different mass numbers).
For example, carbon (C) has three naturally occurring isotopes: carbon-12 (12C), carbon-13 (13C), and carbon-14 (14C). These isotopes have 6 protons (since they are carbon atoms) but different numbers of neutrons: carbon-12 has 6 neutrons, carbon-13 has 7 neutrons, and carbon-14 has 8 neutrons.
So, while all atoms of the same element have the same number of protons (giving them the same atomic number), they can have different numbers of neutrons and, therefore, different mass numbers.