Question

Which one of the following shows highest magnetic moment ?

• A. $F{e}^{2+}$
• B. $C{o}^{2+}$
• C. $C{r}^{3+}$
• D. $N{i}^{2+}$

Answer 1

Answer: (A)

The paramagnetism or magnetic moment produced due to spin of electrons or unpaired cloctrons is expressed in terms of Bohr magneton $(BM)$ or ${\mu }_B$ and given by

Magnetic moment $(\mu )=\sqrt{[n(n+2)]}BM$

where $n$ is the number of unpaired electrons, in species. Thus, greater is the number of unpaired electrons in an ion greater is its paramagnetic nature.

Ion	Electronic configuration	No. of unpaired $e^{-}$ s
$C{r}^{3+}$	$d^3$	3
$F{e}^{2+}$	$d^6$	4
$C{o}^{2+}$	$d^7$	3
$N{i}^{2+}$	$d^8$	2

As $F{e}^{2+}$ ion has maximum number of unpaired electrons, thus it has highest magnetic moment.