Based on the profound effect of the lanthanide contraction, the experimentally established covalent — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Despite Hafnium possessing an entire extra electron shell (principal quantum number $n=6$) compared to Zirconium ($n=5$), the highly ineffective shielding provided by the $14$ fully occupied $4f$ orbitals in Hafnium allows the massive $+32$ increase in nuclear protons to shrink the atomic boundaries drastically. The resulting radius for $Hf$ is approximately $159$ pm, essentially identical to $Zr$ at $160$ pm.