Question

Which of the following is the correct order of ionization energy?

• A. O⁻⁻< F⁻ < Na⁺ < Mg⁺⁺
• B. F⁻< O⁻⁻ < Na⁺ < Mg⁺⁺
• C. O⁻⁻< Na⁺ < F⁻ < Mg⁺⁺
• D. Mg⁺⁺< Na⁺ < F⁻ < O⁻⁻

Answer 1

The correct option is A

O⁻⁻< F⁻ < Na⁺ < Mg⁺⁺

Lets start by calculating number of electrons. [To know whether they are isoelectronic or not]

^{$O^{2-}$} → 10 electrons ^{$F^{-}$} → 10 electrons

^{${Na}^{+}$}→ 10 electrons ^{${Mg}^{++}$}→ 10 electrons

We know that, as number of protons increases, the attraction between electrons (to be removed) and nucleus increases.

That's why atomic radius decreases with the increase in protons.

So, ionization potentials will increase with the increase in number of protons.

Therefore, the correct order of atomic radius will be

^{${Mg}^{2+}$} < ^{${Na}^{+}$}< ^{$F^{-}$}< ^{$O^{2-}$}

Ionization energy:

^{$O^{2-}$} < ^{$F^{-}$} < ^{${Na}^{+}$} < ^{${Mg}^{2+}$}