Which of the following specific pairs of transition elements possess nearly identical atomic radii s — d and f Block Elements Chemistry Question

💡 Solution & Explanation

The poor shielding of the $4f$ electrons (Lanthanoid Contraction) causes the elements of the 5d series to shrink to the size of their 4d counterparts. $Zr$ (4d) and $Hf$ (5d) are classic "chemical twins" with nearly identical radii.