The correct order of the number of unpaired electrons in the ions `Cu^(2+), Ni^(2+), Fe^(3+)`, and `Cr^(3+)`is

Options

A. `Cu^(2+) gt Ni^(2+) gt Cr^(3+) gt Fe^(3+)`
B. `Cr^(3+) gt Fe^(2+) gt Ni^(2+) gt Cu^(2+)`
C. `Fe^(3+) gt Cr^(3+) gt Cu^(2+) gt Ni^(2+)`
D. `Fe^(3+) gt Cr^(3+) gt Ni^(2+) gt Cu^(2+)`

Answer

D

Explanation

`Cr (Z = 24):[Ar] 3d^(5) 4s^(1) rArr Cr^(3+)is [Ar] 3d^(3)`, i.e., `3` unpaired eletrons.
`Fe (Z = 26):[Ar]3d^(6)4s^(2)rArr Fe^(3+)is [Ar] 3d^(8)`, i.e., `2` unpaired electrons.
`Cu (Z = 29):[Ar] 3d^(10)4s^(1) rArr Cu^(2+)is [Ar] 3d^(9)`, i.e., `1` unpaired electron.
Thus, the correct order is
`Fe^(3+) gt Cr^(3+) gt Ne^(2+) gt Cu^(2+)`