Question

$Zr$ (Z=40) and $Hf$ (Z=72) have similar atomic and ionic radii because of :

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Answer 1

As in the lanthanide contraction , when we move from lanthanum to lutetium then the ionic radius gets decreased due to poor shielding effect. Poor shielding effect takes place in 4f electrons . Due to this 6s electrons get attracted towards the nucleus and the size gets decreased .
As , due to lanthanide contraction size of Hafnium is almost getting equal with Zirconium .