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

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Zr (Z = 40) and Hf (Z = 72) have similar atomic and ionic radii because of lanthanoid contraction. Explanation: Zirconium (Zr) and Hafnium (Hf) belong to the same group (Group 4) and have similar chemical properties. However, their atomic and ionic sizes remain almost the same, even though Hf has more protons and electrons. This is due to the lanthanoid contraction, which occurs because of poor shielding by the 4f electrons in the lanthanoid series (which comes between Zr and Hf in the periodic table). As a result, Hf is pulled inward, and its size becomes nearly equal to that of Zr.

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