What is characteristic of isotopes of the same element?

Isotopes of the same element are defined as atoms that have the same atomic number, which means they possess the same number of protons in their nucleus. However, the distinguishing feature of isotopes is that they have different mass numbers due to a varying number of neutrons. While the atomic number remains constant for isotopes of an element, the mass number changes because it is the sum of protons and neutrons. Therefore, the correct characterization of isotopes is that they share the same atomic number but exhibit different mass numbers, highlighting the variance in neutron count while maintaining element identity.

The other options are not applicable because differing atomic numbers would indicate the presence of different elements altogether, which cannot be true for isotopes. Additionally, isotopes generally exhibit similar chemical properties because they have the same electron configuration; thus, their chemical behavior does not significantly differ. Finally, while isotopes do have a different neutron count, they do not have the same neutron count, which is crucial for defining isotopic variation.