Question

The correct order of the number of unpaired electrons in the ions, ${\text{Cu}}^{2+},{\text{Ni}}^{2+},{\text{Fe}}^{3+}\text{and}{\text{Cr}}^{3+}$ is

• A. ${\text{Fe}}^{3+}>{\text{Cr}}^{3+}>{\text{Ni}}^{2+}>{\text{Cu}}^{2+}$
• B. ${\text{Fe}}^{3+}>{\text{Cr}}^{3+}>{\text{Cu}}^{2+}>{\text{Ni}}^{2+}$
• C. ${\text{Cr}}^{3+}>{\text{Fe}}^{3+}>{\text{Ni}}^{2+}>{\text{Cu}}^{2+}$
• D. ${\text{Cu}}^{2+}>{\text{Ni}}^{2+}>{\text{Cr}}^{3+}>{\text{Fe}}^{3+}$

Answer 1

The correct option is A ${\text{Fe}}^{3+}>{\text{Cr}}^{3+}>{\text{Ni}}^{2+}>{\text{Cu}}^{2+}$

Electronic configuration of the following ions are :
$C{u}^{2+}:\left[Ar\right]3d^{9}4s^0$
$N{i}^{2+}:\left[Ar\right]3d^{8}4s^0$
$F{e}^{3+}:\left[Ar\right]3d^{5}4s^0$
$C{r}^{3+}:\left[Ar\right]3d^{3}4s^0$
The number of unpaired electrons in the given ions is:
$C{u}^{2+}\to 3d^9\to \text{Number of unpaired electrons = 1}$
$N{i}^{2+}\to 3d^8\to \text{Number of unpaired electrons = 2}$
$F{e}^{3+}\to 3d^5\to \text{Number of unpaired electrons = 5}$
$C{r}^{3+}\to 3d^3\to \text{Number of unpaired electrons = 3}$
The correct order of the number of unpaired electrons is: ${\text{Fe}}^{3+}>{\text{Cr}}^{3+}>{\text{Ni}}^{2+}>{\text{Cu}}^{2+}$