Although Zirconium belongs to the 4d transition series and Hafnium to 5d
transition series even then they show similar physical and chemical properties
(i) both belong to d-block.
(ii) both have the same number of electrons.
(iii) both have a similar atomic radius.
(iv) both belong to the same group of the periodic table
Option (iii) both have a similar atomic radius is the answer