Name the species that will be isoelectronic with the following atoms or ions.
(i) Na (ii) ${{Cl}^{-}}$ (iii)${{Ca}^{2+}}$ (iv)${{Rb}^{+}}$
Isoelectronic species are those which have same number of electrons.
(i) Ne has 10 electrons. Therefore, the species ${{N}^{3-}}$, ${{O}^{2-}}$, ${{F}^{-}}$, ${{Mg}^{2+}}$, ${{Al}^{3+}}$ etc., each of which has also 10 electrons are isoelectronic with it.
(ii) Cl has 18 electrons. Therefore, the species ${{P}^{3-}}$ , ${{S}^{2-}}$ , Ar, ${{K}^{+}}$ and ${{Ca}^{2+}}$, each one of which contains 18 electrons are isoelectronic with it.
(iii) ${{Ca}^{2+}}$ has 18 electrons. Therefore, the species ${{P}^{3-}}$ , ${{S}^{2-}}$, Ar and ${{K}^{+}}$, each of which also contains 18 electrons are isoelectronic with it.
(iv) ${{Rb}^{+}}$ has 36 electrons. Therefore, the species, ${{Br}^{-}}$, Kr or ${{Sr}^{2+}}$ each of which also has 36 electrons, are isoelectronic with it."