All the isotopes of an element have the same _________ but different ___________.

All the isotopes of an element have the same atomic number but different mass numbers.

Isotopes are atoms that belong to the same element. The atoms of the same element having the same atomic number but different mass numbers are called isotopes. For example, carbon-14, carbon-13, and carbon-12 are isotopes of carbon, all of these isotopes have atomic number 6 but different mass numbers 14, 13, and 12 respectively.