what are isotones

Isotones are atoms or nuclei that have the same number of neutrons but different numbers of protons. For example, boron-12 and carbon-13 nuclei both contain 7 neutrons, and so are isotones. Similarly, 36S, 37Cl, 38Ar, 39K, and 40Ca nuclei are all isotones of 20 because they all contain 20 neutrons. Isotones are different from isotopes, which are atoms or nuclei that have the same number of protons but different numbers of neutrons, and isobars, which are atoms or nuclei that have the same mass number but different atomic numbers.