Question

Explain why:
Zr and Hf exhibit similar properties.
(At. no. of Zr = 40, Hf = 72)

Answer 1

The transition metals of third series ($Hf$) have nearly the same radii as that of second transition series ($Zr$) due to the phenomenon called lanthanoid contractions which involves filling of f- orbitals. Because of the weak screening or shielding effect of f-orbital electrons in $Hf$ the effective nuclear charge on valance electrons is similar to that on $Zr$ and therefore results in similar properties.