What are isotopes?

Isotopes are defined as atoms that have the same number of protons but different numbers of neutrons. This means that while isotopes of an element share the same atomic number and thus belong to the same element, they differ in their mass due to the differing number of neutrons. For example, carbon has several isotopes, including carbon-12 and carbon-14; both have six protons, but carbon-12 has six neutrons while carbon-14 has eight. This distinction not only helps in identifying different isotopes, but it also has practical implications in fields like radiometric dating and medical imaging, where specific isotopes are used for their radioactive properties.

In contrast, options indicating different elements, different numbers of electrons, or varying physical states do not accurately describe isotopes. Different elements have different atomic numbers, different numbers of electrons pertain to ions rather than isotopes, and physical states relate to the states of matter rather than the structure of an atom.