Identify the correct order of increasing ionic sizes

A
${Al}^{3 +} < O^{2 -} < F^{-} < {Cl}^{-}$
B
$F^{-} < O^{2 -} < {Cl}^{-} < {Al}^{3 +}$
C
${Al}^{3 +} < F^{-} < O^{2 -} < {Cl}^{-}$
D
${Al}^{3 +} < F^{-} < {Cl}^{-} < O^{2 -}$

Solution:

The electronic configurations of the given ions are

${Al}^{3 +} : (1 s)^{2} (2 s)^{2} (2 p)^{6} F^{-} : (1 s)^{2} (2 s)^{2} (2 p)^{6}$

$O^{2 -} : (1 s)^{2} (2 s)^{2} (2 p)^{6} {Cl}^{-} : (1 s)^{2} (2 s)^{2} (2 p)^{6} (3 s)^{2} (3 p)^{6}$

The size of ${Cl}^{-}$ will be the largest as its outer shell belongs to the quantum number n = 3. Of the remaining species,

${Al}^{3 +}$ will have the minimum ionic size because of three positive charge and $O 2^{-}$ will have maximum ionic size because of two negative charge.

Solution:

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