Zr is in 4d-series, Hf is in 5d-series. But their atomic radii is same

1.	Zr is in 4d-series, Hf is in 5d-series. But their atomic radii is same. Why?
Answer» Solution :Same radii of Zr and HF is DUE to lanthanide contraction. Elements whose 4f is filled have abnormal small SIZES, because of the ineffective screening by inner f-orbitals.

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