Which of the following atomic species has maximum ionisation energy? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Compare the Group 16 anions (O^-, S^-, Se^-, Te^-). Ionization energy of an anion corresponds to the energy required to remove the added electron, which is equal in magnitude to the electron affinity of the neutral atom. Step 2: Due to the exceptionally small size of the Oxygen atom, added electrons experience high electron-electron repulsion, which lowers its electron affinity compared to Sulfur. Step 3: Sulfur has the highest electron affinity (and thus S^- has the highest ionization energy) among the group members. Since size increases further down the group from S to Te, S^- has the maximum ionization energy.