Isotopes, Atomic Mass and Isobars

Apart from oxygen-$16$, oxygen-$17$ and oxygen-$18$ are also known to exist in nature. Are these atoms isotopes or isobars? Explain.

${}_8{}^{16}\mathrm{O}$ and ${}_7{}^{16}\mathrm{N}$ are isobars. Use this example to explain isobars.

Isotopes have different: