Question

Which of the following pairs of elements have almost similar atomic radii ?
(1) $Zr , Hf$
(2) $Mo, W$
(3) $Co, Ni$
(4) $Sn , Pb$

• A. 1, 2 and 3 are correct
• B. 1 and 2 are correct
• C. 2 and 4 are correct
• D. 1 and 3 are correct

Answer 1

Answer: (A)

The atomic radii of $Zr$ and $Hf$ and $Mo$ and $W$ are similar due to lanthanide contraction. In case of $Co$ and $Ni$ the effect of increased nuclear charge is almost balanced by the increase in size due to increasing shielding effect, hence the atomic radii of $Co$ and $Ni$ are nearly same.