Question

why is the atomic radius of Hf and Zr are nearly same?​

Answer 1

Answer:

Zr and Hf have almost identical atomic radii due to lanthanoid contraction. Hf is post lanthanoid element. As a result of lanthanoid contraction, the atomic size of Hf is similar to Zr ( element of previous period)

Answer 2

We all know that going down the group the atomic radius of elements  increases .

But there is an exception -

The Shielding effect of Zr is more than the shielding effect  of Hf . So the  size of radii of Zr and Hf are nearly dame