Question

Which of the following ions has the least magnetic moment?

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

Answer 1

Answer: (A)

Ion	Electronic configuration	No. of unpaired electrons
$C{u}^{2+}$	$d^9$	$1$
$N{i}^{2+}$	$d^8$	$2$
$C{o}^{2+}$	$d^7$	$3$
$F{e}^{2+}$	$d^6$	$4$

Magnetic moment $(\mu )=\sqrt{n(n+2)}BM$
Here $n=$ number of unpaired electrons.
(a) Magnetic moment of $C{u}^{2+}$,
$\mu =\sqrt{1(1+2)}BM$
$=1.73BM$
(b) Magnetic moment of $N{i}^{2+}$,
$\mu =\sqrt{2(2+2)}BM$
$=2.84BM$
(c) Magnetic moment of $C{o}^{2+}$,
$\mu =\sqrt{3(3+2)}BM$
$=3.86BM$
(d) Magnetic moment of $F{e}^{2+}$,
$\mu =\sqrt{4(4+2)}BM$
$=4.90BM$
Hence, $C{u}^{2+}$ has only one unpaired electron.
Therefore, $C{u}^{2+}$ has least magnetic moment.