The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively. Hope I helped u.. Plz mark as the BRAINLIEST answer if helpful..
1 5 1
Atoms of the same element with different mass numbers are called ISOTOPES
eg : C-12 , C-13, C-14
2 3 2