Zr ( Z = 40 ) and Hf ( Z = 72 ) have similar atomic and ionic radii because of:
and have similar atomic and ionic radii because of:
belonging to same group
diagonal relationship
lanthanoid contraction
having similar chemical properties
Solution
and have similar atomic and ionic radii because of Lanthanoid Contraction. The orbital offers very poor screening. So, the radius (atomic as well as Ionic) of and are almost the same.