Question

Although Zirconium belongs to $4d$ transition series and Hafnium to $5d$ transition series even then they show similar physical and chemical properties because ___________.

• A. both have similar atomic radius.
• B. both belong to $d-$block.
• C. both have same number of electrons.
• D. both belong to the same group of the periodic table.

Answer 1

The correct option is A

both have similar atomic radius.

Lanthanoid contraction is the phenomenon by which the size of the atoms decreases with an increase in the atomic number. As the atomic number increases in the lanthanide series, the nuclear charge increases due to the poor shielding effect of $f-$orbitals. So, the electrons come closer, and the size of the atoms decreases.

Due to lanthanoid contraction, Zirconium $(Z=40)$ and Hafnium $(Z=72)$ have similar atomic radii, due to which they show similar physical and chemical properties.​

So, option $\left(C\right)$ is the correct answer.