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

Answer 1

Hint: Consider the effect of lanthanide contraction. Lanthanide contraction is an unusual decrease in the atomic/ionic radii of lanthanide elements with increase in the atomic number.

Complete answer:
The following is the arrangement of some d block elements. These elements belong to group Group 3 and Group 4 in the Periodic table.

Sc	Ti
Y	Zr
La	Hf

Yttrium and lanthanum are placed below scandium.
Similarly, Zirconium and hafnium are placed below titanium.
Between lanthanum and hafnium, fourteen f block elements are present. In these elements, the last electron enters (n-2)f subshell, which is a part of the inner core. The electron density and nuclear charge increases but the number of shells remains. Due to this, the contraction of the outermost shell also increases. The electrons of (n-2)f subshell, poorly shield the outermost shell electrons from the nuclear charge. This decreases the screening of the nuclear charge. Due to this, the outermost electrons experience high attraction from the nucleus. Therefore, on moving from left to right in the series, the size gradually decreases. This contraction in the size is due to lanthanide elements. Hence, the contraction is called lanthanoid contraction.
Hafnium has one more shell than zirconium. But the radius of hafnium is almost the same as that of zirconium. This is due to lanthanoid contraction. Due to similar atomic size, zirconium and hafnium show almost similar physical and chemical properties.

Hence, the correct option will be the option C ) both have similar atomic radius.

Note: Due to lanthanoid contraction, the basic character of hydroxides decreases. Also, the second and third transition metal elements have similar size. Due to lanthanoid contraction, the lanthanoids can be separated by ion exchange method.