Which among the following species have the same number of electrons in its outermost as well as penultimate shell

Which among the following species have the same number of electrons in

1.	Which among the following species have the same number of electrons in its outermost as well as penultimate shell
Answer» `Mg^(2+)` `O^(2-)` `F^-` `CA^(2+)` Solution :`._20Ca=2,8,8,2` `Ca^(2+)` =2,8,8 Hence, `Ca^(2+)` has 8 electrons each in outermost and PENULTIMATE SHELL.