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^(+)` and `Mg^(2+)` are iso-electronic species (have 10 electrons) `K^(+), Ca^(2+), S^(2-)` are iso-electronic species (have 18 electrons)