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

Explanation

`Na^+, Mg^(2+)`
`K^+, Ca^(2+), S^(2-)` and Ar are isoelectronic.