Which of the following pairs of elements exhibit almost identical atomic radii exclusively as a cons — d and f Block Elements Chemistry Question

💡 Solution & Explanation

The lanthanoid contraction is the steady decrease in size of the lanthanides (from $Ce$ to $Lu$), effectively cancelling out the expected size increase when moving from the $4d$ to the $5d$ series. Thus, post-lanthanide pairs like $Zr/Hf$, $Nb/Ta$, and $Mo/W$ have nearly identical atomic radii. $Y$ and $La$ do not share identical radii because $La$ appears before the $4f$ orbital begins filling, so it is unaffected by the contraction.