An increase in both atomic and ionic radii with atomic number occurs in any group of the perioidc table and in accordance with this, the ionic radii of Ti (IV) and Zr (IV) ionc are 0.68 A^(@) and 0.74A^(@) respectively, but for Hf (IV) ion the ionic radius of 0.75A^(@), which is almost the same as that for Zr (IV) ion. This is due to

An increase in both atomic and ionic radii with atomic number occurs i

1.	An increase in both atomic and ionic radii with atomic number occurs in any group of the perioidc table and in accordance with this, the ionic radii of Ti (IV) and Zr (IV) ionc are 0.68 A^(@) and 0.74A^(@) respectively, but for Hf (IV) ion the ionic radius of 0.75A^(@), which is almost the same as that for Zr (IV) ion. This is due to
Answer» greater degree of covalency in compounds of `Hf^(4+)` alntanide contraction difference in the COORDINATION NUMBER of `Zr^(4+) and Hf^(4+)` in their compounds actinide contraction. Solution :Normal size increase on moving down the group from Zr to Hf is ALMOST exactly balanced by lanthanide contraction. Lanthanide contraction is the steady decrease in the RADII as atomic number of lanthanide elements increases.