Iye awon nukleoni (protons ati neutrons) ninu nukleu ni nomba akojo, 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.. 
Open Amerika àwọn obìnrin DokewòọnnOpen Amẹrika gẹgẹbi ọdun.. 