Which of the following metal is expected to have the highest third ionization enthalpy? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Write down the electronic configurations of the divalent M^2+ ions of these transition metals: Cr^2+ ([Ar] 3d^4), V^2+ ([Ar] 3d^3), Mn^2+ ([Ar] 3d^5), and Fe^2+ ([Ar] 3d^6). Step 2: The divalent Manganese ion (Mn^2+) possesses an exactly half-filled d-subshell ([Ar] 3d^5), which is exceptionally stable due to symmetrical distribution of electron density and high exchange energy. Step 3: Removing an electron from this stable half-filled configuration to form Mn^3+ requires a very high amount of energy, making Manganese have the highest third ionization enthalpy.