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

`{:("No. of electrons are :",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, isoelectronic species are `Na^(+)` and `Mg^(2+), K^(+), Ca^(2+), S^(2-)` and `Ar`,