JAMB - Chemistry (2019 - No. 56)
The following are isoelectronic ions except
Na\(^+\)
Mg\(^{2+}\)
Si\(^{2+}\)
O\(^{2+}\)
Paliwanag
Two or more ions are said to be isoelectronic if they have the same electronic structure and the same number of valence electrons.
Na\(^+\) = 10 electrons = 2, 8
Mg\(^{2+}\) = 10 electrons = 2,8
O\(^{2-}\) = 10 electrons = 2,8
Si\(^{2+}\) = 12 electrons = 2,8,2
\(\implies\) Si\(^{2+}\) is not isoelectronic with the rest.