Question

Which has least covalent radius.

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• A. $Cu$
• B. $Mn$
• C. $Ni$
• D. $Zn$

Answer 1

The correct option is C $Ni$

The elements are d-block elements and they show the effect in their radius due to the partially-filled and full-filled d-orbitals also. The atomic radius is more for the elements with these configurations and so they show irregularities in the trend.
As the unpaired electrons increase, the attraction increases due to metal-metal bonding and so the size decreases due to decrease in the bond length. This contradicts the normal behavior of the size of the atom.
So, the size decreases initially, then remains constant and later on increases. The size for the given period of the atom is maximum for Sc and it decreases till $Mn$. Then it remains almost constant till $Ni$ and then again increases uptil $Zn$
So, $Ni$ has the least covalent radius among the following given elements and the correct option is (d).
Covalent radius in $pm$
$Ni<Cu<Zn=Mn125128137137$