Question

The size of hafnium is almost similar to that of zirconium, this is due to:
A.Increase in size as expected
B.Decrease in size as expected
C.Lanthanide contraction
D.Similar chemical properties

Answer 1

Hint: The element hafnium has been denoted by the symbol Hf and its atomic number is 72. The element zirconium has been denoted by the symbol Zr and its atomic number is 40.

Complete answer:
The periodic table is the table of elements where all the elements are arranged periodically according to their repeating properties. The elements are sequenced as per their atomic numbers. This is the modern periodic table and it is also known as the long form of periodic table.
The modern periodic table consists of seven rows and eighteen columns. These seven rows are known as periods whereas the eighteen columns are known as groups. Each group comprises elements with similar chemical nature and in each period, the physical and chemical properties transition from left to right.
The atomic size or the atomic radius is the distance between the center of the nucleus of the atom and its outermost electron or the outermost shell. The atomic size increases from top to bottom in the group and it decreases from left to right across the period.
The lanthanide series comprises fifteen chemical elements with atomic numbers 57 to 71. This series is located at group three and period five. It starts at element Lanthanum and ends at element Lutetium. Lanthanide contraction is a greater than expected decrease in atomic size of the elements in the lanthanide series.
This lanthanide contraction is due to the poor shielding of nuclear charge by the 4f electrons. Thus, resulting in the decrease in the atomic size. Due to the lanthanide contraction, the size of hafnium decreases such that it becomes similar with that of zirconium.

Therefore, the correct answer is option C.

Note:
This series of lanthanide contraction Cerium(Ce), Praseodymium(Pr), Neodymium(Nd), Promethium(Pm), Samarium(Sm), Europium(Eu), Gadolinium(Gd), Terbium(Tb), Dysprosium(Dy), Holmium(Ho), Erbium(Er), Thulium(Tm), Ytterbium(Yb), and Lutetium(Lu).The effect of lanthanide contraction is also seen in the similar sizes of Molybdenum and Tungsten.