Which of the following are isoelectronic species i.e., those having the same number of electrons?
`Na^(+),K^+,Mg^(2+),Ca^(2+),S^(2-),Ar`.

Explanation

Number of electrons present in `Na^(+)(11-1)=10,K^(+)=(19-1)=18,Mg^(2+)=(12-2)=10,Ca^(2+)=(20-2)=18,S^(2-)=(16+2)18,Ar=18`. Hence, `Na^(+) and Mg^(2+)` are isoelectronic because they contain 10 electrons each. `K^(+),Ca^(2+),S^(2-)` and Ar are isoelectroniic because they contain 18 electrons each.