The second ionization energy is maximum for : — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Write the electronic configurations of the monovalent cations (M^+): B^+ (1s2 2s2), Be^+ (1s2 2s1), Mg^+ ([Ne] 3s1), and Al^+ ([Ne] 3s2). Step 2: The second ionization energy involves removing an electron from these cations. B^+ has a completely filled stable 2s^2 shell of a smaller principal quantum number (n=2) compared to Mg^+ or Al^+ (n=3). Step 3: Disrupting the stable, fully-filled 2s subshell of the small B^+ cation requires the greatest amount of energy, making Boron have the highest second ionization energy.