Question

Which one of the following is the correct order of the size of the ions ?

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

Answer 1

The correct option is B $O^{2-}>F^{-}>N{a}^{+}>M{g}^{2+}$

As, all the species have the same number of the shell, i.e. there are 2 shells in each species.

Now, when all species have the same number of the shell, then the higher the positive charge more the effective nuclear charge, hence the smaller the size and higher negative charge lesser the effective nuclear charge so larger the size.

Hence the order is as follows:
$O^{2-}>F^{-}>N{a}^{+}>M{g}^{2+}$