Question

In isoelectronic series, which of the following will be the smallest?

• A. $O^{2-}$
• B. $F^{1-}$
• C. $Ne$
• D. $N{a}^{1+}$
• E. $M{g}^{2+}$

Answer 1

Answer: (E)

$M{g}^{2+}$

Since, the number of electrons are same, size is determined by the number of protons. The atom with greatest nuclear charge pulls the electrons closer, thus, is the smallest.

The $O^{2-}$ has $8$ protons and the nuclear charge is the smallest of the series. Thus, it has the least "pull" on the electrons and this species is the largest.

$M{g}^{2+}$ has $12$ protons and the nuclear charge is highest and thus this will be the smallest.