Question

The ions $ {{N}^{3-}},{{O}^{2-}},{{F}^{-}},N{{a}^{+}}M{{g}^{2+}} $ are isoelectronic. Their ionic radii show

• A. an increase from $ {{N}^{3-}} $ to $ {{F}^{-}} $ and then decrease from $ N{{a}^{+}} $ to $ M{{g}^{2+}} $
• B. a decrease from $ {{N}^{3-}} $ to $ {{F}^{-}} $ and then increase from $ N{{a}^{+}} $ to $ M{{g}^{2+}} $
• C. a significant increase from $ {{N}^{3-}} $ to $ M{{g}^{2+}} $
• D. a significant decrease from $ {{N}^{3-}} $ to $ M{{g}^{2+}} $

Answer 1

Answer: (D)

Ionic radii
$ \propto \frac{1}{effective\text{ }nuclear\text{ }ch\arg e({{Z}_{eff}})} $
$ \propto negative\text{ }charge $
$ \propto \frac{1}{positive\text{ }charge} $
Hence, as the negative charge increases, ionic radii increases and with increase in positive charge ionic radii decrease. Hence, ionic radii decreases from
$ {{N}^{3-}} $ to $ M{{g}^{2+}} $