Which of the following d-block elements has the bigger covalent radius ?

Options

A. Co
B. Ni
C. Cu
D. Zn

Answer

B

Explanation

Co (116 pm) gt Ni (115 pm) lt Cu (117 pm) lt Zn (125 pm)
As we move form alkali metals to alkaline earth metals and form alkain earth metals to the d-block metals, the atomic radii decrease steeply but within d-block elements this rate of decrease is less due to increase in the number of inner shielding electrons. However, the general trend of decreasing size is reversed towerds the ends of the series due to an increase in inter-electronic repulsion a after the addition of sufficient number of electrons in the (n-1) d orbitals leading to the gradual increase in size. Other examples
Rh(125 pm) lt pd(128) lt Ag(134) lt Cd(141)
Ir(126 pm) lt Pt(129) lt Au(134) lt Hg(144)