Question

define what is meant by the term isotope?​

Answer 1

Answer:

each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.

"some elements have only one stable isotope"

Answer 2

Isotopes are the elements which have same atomic number but different atomic masses