In which of the following pairs, the ions are isoelectronic?

For, Na+ = 11-1 = 10e-      Mg2+ = 12-2 = 10e-Thus, they have same number of electrons.For, Al3+=13-3=10e-,O-=8+1=9e-They do not have same number of electrons.For, Na+ = 10 e-     O2- = 8+2 = 10 e-They have same number of electrons.For N3- = 7+3 = 10 e-, Cl- = 17+1 = 18e-They do not have same number of electrons.Thus, Na+ is isoelectronic with Mg2+ and O2-