• # question_answer 21) What do you understand by isoelectronic species? Name a species that will be isoelectronic with each of the following atoms or ions: (i) ${{F}^{-}}$ (ii) $Ar$ (iii) $M{{g}^{2+}}$ (iv) $R{{b}^{+}}$

Ions of different elements which have same number of electrons but differ from one another in magnitude of nuclear charge are known as isoelectronic species. (i) ${{F}^{-}}$ has 10 electrons. Isoelectronic species: $N{{a}^{+}},M{{g}^{2+}},A{{l}^{3+}},{{N}^{3-}},{{O}^{2-}}$ (ii) Ar has 18 electrons. Isoelectronic species: ${{K}^{+}},C{{a}^{2+}},{{P}^{3-}},{{S}^{2-}},C{{l}^{2-}}$ (iii) $M{{g}^{2+}}$ has 10 electrons. Isoelectronic species: $N{{a}^{+}},A{{l}^{3+}},{{N}^{3-}},{{O}^{2-}},{{F}^{-}}$ (iv) $R{{b}^{+}}$ has 36 electrons. Isoelectronic species: $S{{r}^{2+}},Kr,B{{r}^{-}}S{{e}^{2-}},A{{s}^{3-}}$