Question

Atomic size increase down the group but 4th group of the periodic table zr ,hf almost the same atomic size

Answer 1

Due to lanthanoid contraction.
As after lanthanum electron filling take place in f subshell.
Electrons present in f subshell didn't do good shielding due to which with the increasing atomic number or increasing effective nuclear charge size gets constricted and size of Halfenium and Zirconium becomes almost equal.
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