Question

Which of the following statements is incorrect for pairs of elements \[Zr-Hf\]?
A.Both possess the same number of valence electrons
B.Both have identical atomic sizes
C.Both have almost identical ionic radius
D.Both of these belong to the same period of periodic table

Answer 1

Hint:In the question we have \[Zr - Hf\]. These elements belong to the transition group. Transition elements (also known as transition metals) are elements that have partially filled d orbitals. IUPAC defines transition elements as an element having a d subshell that is partially filled with electrons, or an element that has the ability to form stable cations with an incompletely filled d orbital.

Complete answer:
The first element in the given pair is Zirconium. Zirconium is a chemical element with the symbol $Zr$ and atomic number 40. It is a lustrous, grey-white, strong transition metal.
The second element in the given pair is Hafnium. Hafnium is a chemical element with the symbol $Hf$ and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals.
The first option is about the number of valence electrons. As both the elements belong to the same group so both will have the same number of valence electrons. So the first option is correct.
The second option is about identical atomic size. The elements in the same group have a similar property. So \[Zr-Hf\] have similar atomic size. So the second option is correct.
The third option is about identical ionic radius. The elements in the same group have the same valency. So they will form the same type of ions. Also on moving down the group the ionic radius decreases, but as the atomic number increases this trend decreases. So the element has identical ionic radius. So the third option is also correct.
In the fourth option it is asked about the period. As the elements are in the same group so they are not in the same period. So the period is different. So the fourth option is incorrect.

So, the answer to the above question is D.

Note:
The periodic table, also known as the periodic table of elements, is a tabular display of the chemical elements, which are arranged by atomic number, electron configuration, and recurring chemical properties. There are four blocks. S block represents alkali metals and alkaline earth metals. P block represents group 17 and group 18. D block represents the transition metals. F block represents the inner transition elements like lanthanoids and actinoids.