The first, second and third ionisation energies (E1, E2 & E3) for an element are 7eV, 12.5eV and 42. — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Compare the successive ionization energy differences: E_2 - E_1 = 5.5 eV, whereas E_3 - E_2 = 30 eV. Step 2: The very large gap between E_2 and E_3 indicates that the third electron must be removed from a highly stable, closed inner shell. Step 3: Therefore, the element has two easily removable valence electrons, making the +2 oxidation state the most stable.