Q. Which among the following species have the same number of electrons in its outermost as well as penultimate shell?
A) $Mg^{2 +}$
B) $O^{2 -}$
C) $F^{-}$
D) $Ca^{2 +}$
Explanation
(d)
$\ _{20}Ca = 2,\ 8,\ 8,\ 2$
$Ca^{2 +} = 2,\ 8,\ 8$
Hence, $Ca^{2 +}$ has 8 electrons each in outermost and penultimate shell.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.