Question

Because of lanthanoid contraction, which of the following pairs of elements have nearly same atomic radii? (Numbers in the brackets are atomic numbers)

• A. $Zr\left(40\right)$ and $Nb\left(41\right)$
• B. $Zr\left(40\right)$ and $Hf\left(72\right)$
• C. $Zr\left(40\right)$ and $Ta\left(73\right)$
• D. $Ti\left(22\right)$ and $Zr\left(40\right)$

Answer 1

Answer: (A)

$Zr\left(40\right)$ and $Nb\left(41\right)$

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.

Hence option B)$Zr\left(40\right)-and-Hf\left(72\right)$