WAEC Chemistry 2024 Paper

Concept:Species with the same number of electrons are known as isoelectronic species.Explanation:For $_8\mathrm{X}^{2-}$, the atomic number is $8$, so it has $8$ protons.Since it carries a $2-$ charge, it gains $2$ electrons.Therefore, number of electrons in $_8\mathrm{X}^{2-} = 8 + 2 = 10$.For $_{10}\mathrm{Y}$, the atomic number is $10$, so it has $10$ protons.It has no charge, meaning it is a neutral atom.Therefore, number of electrons in $_{10}\mathrm{Y} = 10$.Both species contain $10$ electrons, even though they are different elements with different proton numbers.Thus, they have the same electronic configuration.Answer:$_8\mathrm{X}^{2-}$ and $_{10}\mathrm{Y}$ are isoelectronic species.