In two elements ${}_{{\mathrm{z}}_1}\mathrm{A}^{{\mathrm{M}}_1}$and ${}_{{\mathrm{z}}_2}B^{{\mathrm{M}}_2}$${\mathrm{M}}_1\ne {\mathrm{M}}_2$ and ${\mathrm{Z}}_1\ne {\mathrm{Z}}_2$ $\mathrm{but} {\mathrm{M}}_1-{\mathrm{Z}}_1={\mathrm{M}}_2-{\mathrm{Z}}_2$. These elements are

Isotones are the atoms of different elements which have same no. of neutrons.

$\mathrm{Ex}:{}_6{}^{14}\mathrm{C} \mathrm{and} {}_8{}^{16}\mathrm{O}.$

The no. of neutrons = 8.