\(O ^{-2}\) | \(F ^{-}\) | \(Na ^{+}\) | \(Mg ^{2+}\) | |
\(Z\) | \(8\) | \(9\) | \(11\) | \(12\) |
\(e^{-}\) | \(10\) | \(10\) | \(10\) | \(10\) |
\(\frac{z}{e}\) | \(0.8\) | \(0.9\) | \(1.1\) | \(1.2\) |
as \(\frac{z}{e}\) ratio increases size decreases.
Thus correct ionic radiit order is \(O ^{-2}> F ^{-}> Na ^{+}> Mg ^{2+}\)
Therefore correct option is \((4)\)