Question

Which one of the following is correct order of second ionisation potential of $Na,Ne,Mg$ and $Al$ ?

• A. Al < Na < Mg < Ne
• B. Ne < Al < Na < Mg
• C. Mg < Al < Ne < Na
• D. Na < Mg < Ne < Al

Answer 1

Answer: (C)

The electronic configuration of $Na,Ne,Mg$ and $Al$ after the removal of an electron is as

$N{a}^{+}:1s^2,2s^2,2p^6$

$N{e}^{+}:1s^2,2s^2,2p^5$

$M{g}^{+}:1s^2,2s^2,2p^6,3s^1$

$A{l}^{+}:1s^2,2s^2,2p^6,3s^2$

The ionisation energy decreases as the size of the atom/ion increases. Further ionisation energy increases with increase in nuclear charge. Since, $N{a}^{+}$ gives a stable electronic configuration hence its $I{E}_2$ is highest among the given species and therefore the correct order of their $I{E}_2$ is

$Mg<Al<Ne<Na$