Which of the following is the best description of an isotope?

An isotope is a variant of a particular chemical element, which shares the same number of protons, or atomic number, but has a different number of neutrons, resulting in a different atomic mass. This means that while they are the same element, they have different physical properties due to the difference in mass. Some isotopes are stable, while others are radioactive and decay over time, which is useful in fields like radiometric dating.