Which of the following pairs of transition elements definitively exhibit nearly identical atomic and — d and f Block Elements Chemistry Question

💡 Solution & Explanation

The lanthanoid contraction involves the poor shielding of the 14 $4f$ electrons, which causes the elements of the $5d$ transition series (post-lanthanum) to shrink down to sizes virtually identical to their $4d$ counterparts. Therefore, $Zr \approx Hf$, $Nb \approx Ta$, and $Mo \approx W$. Yttrium ($Y$) and Lanthanum ($La$) belong to Group 3 and are unaffected because $La$ comes *before* the $4f$ filling begins.