Analyzing the vertical group trends in the d-block, it is observed that the first ionization energie — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Typically, $IE$ drops down a group. However, in the d-block, the $5d > 4d > 3d$ trend dominates because the highly diffuse $4f$ electrons are terrible shields. The resulting spike in Effective Nuclear Charge holds the outer $6s$ electrons extremely tightly.