WAEC - Chemistry (2024 - No. 34)

Isoelectronic species are atoms, ions, or molecules that have the same number of electrons and therefore, the same electronic configuration, even if they are different elements. 

For \(_8\)X\(^{2-}\) 

Number of protons = 8, while Number of electrons = 10, because X gains 2 electrons and outnumbers the number of protons.

Also, for \(_{10}\)Y,

Number of protons = 10, while Number of electrons = 10, because Y has no charge, it is a neutral atom. Hence, the number of protons = Number of electrons =10 

Since the number of electrons are the same in both atoms of element X and element Y, even though they are of different elements, they are said to be isoelectronic species.

Therefore, \(_8\)X\(^{2-}\) and \(_{10}\)Y are Isoelectronic