${}_6{}^{12}\mathrm{C},{}_6{}^{13}\mathrm{C},{}_6{}^{14}\mathrm{C}\text{ and }{}_{17}{}^{35}\mathrm{Cl},{}_{17}{}^{37}\mathrm{Cl}$ are the examples of

${}_6{}^{12}\mathrm{C},{}_6{}^{13}\mathrm{C},{}_6{}^{14}\mathrm{C}\text{ and }{}_{17}{}^{35}\mathrm{Cl},{}_{17}{}^{38}\mathrm{Cl}$ are the isotopes of C and Cl, respectively.

(same atomic no. different mass no.)