Question

The substances which contain species with unpaired electrons in
their orbitals behave as paramagnetic substances. Such substances
are weakly attracted by the magnetic field. The paramagnetism is
expressed in terms of magnetic moment. The magnetic moment is
related to the number of unpaired electrons according to the
following relation:
Magnetic moment, $\mu =\sqrt{n(n+2)}BM$
where, $n=$ number of unpaired electrons.
$BM$ stands for Bohr magneton, a unit of magnetic moment.
$1BM=\frac{eh}{4\pi mc}=9.27\times {10}^{-24}{Am}^2$ or $J{T}^{-1}$

In which of these options do both constituents of the pair have the same magnetic moment?

• A. ${Zn}^{2+}$ and ${Cu}^{+}$
• B. ${Co}^{2+}$ and ${Ni}^{2+}$
• C. ${Mn}^{4+}$ and ${Co}^{2+}$
• D. ${Mg}^{2+}$ and ${Sc}^{+}$

Answer 1

Answer: (A), (C)

The correct options are
A ${Zn}^{2+}$ and ${Cu}^{+}$
C ${Mn}^{4+}$ and ${Co}^{2+}$

(A) $Z{n}^{2+}$ and $C{u}^{+}$ have the same magnetic moment as they have same number of unpaired electrons.
$Z{n}^{2+}3d^{10}0$ unpaired electrons.
$C{u}^{+}3d^{10}0$ unpaired electrons.
(B)
$C{o}^{2+}$ and $N{i}^{2+}$ have different magnetic moment as they have different number of unpaired electrons.
$C{o}^{2+}3d^{7}3$ unpaired electrons.
$N{i}^{2+}3d^{8}2$ unpaired electrons.
(C)
$M{n}^{4+}$ and $C{o}^{2+}$ have the same magnetic moment as they have same number of unpaired electrons.
$C{o}^{2+}3d^{7}3$ unpaired electrons.
$M{n}^{4+}3d^{3}3$ unpaired electrons.
(D)
$M{g}^{2+}$ and $S{c}^{+}$ have different magnetic moment as they have different number of unpaired electrons.
$M{g}^{2+}3d^{0}0$ unpaired electrons. Mg is not a transition element. So it lacks d electrons.
$S{c}^{+}3d^{2}2$ unpaired electrons.