Final answer:
Isotopes are atoms of the same element that contain different numbers of neutrons. They have the same number of protons and electrons but differ in overall weight.
Step-by-step explanation:
Isotopes are atoms of the same element that contain different numbers of neutrons. The overall charge of an isotope is not different from the standard atom of the element, so option a) is incorrect. Isotopes have the same number of protons and electrons, so option b) and option c) are characteristics of isotopes. The only characteristic that is not true for isotopes is that their overall weight is different, making option d) the correct answer.