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 $J{T}^{-1}$

Which of the following ions are diamagnetic?

• A. ${He}^{2+}$
• B. ${Sc}^{3+}$
• C. ${Mg}^{2+}$
• D. $O^{2-}$

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A ${He}^{2+}$
B ${Sc}^{3+}$
C ${Mg}^{2+}$
D $O^{2-}$

All of the following ions are diamagnetic as they have 0 unpaired electrons.
$H{e}^{2+}$ has 0 electrons. The number of unpaired electrons is 0.
$S{c}^{3+}$ has electronic configuration $\left[Ar\right]$. The number of unpaired electrons is 0.
$M{g}^{2+}$ has electronic configuration $\left[Ne\right]$. The number of unpaired electrons is 0.
$O^{2-}$ has electronic configuration $\left[Ne\right]$. The number of unpaired electrons is 0.
Note: If one or more unpaired electrons are present, then the species is paramagnetic.