Paramagnetic substances are attracted by an external magnetic field, that is, they move from a weaker to a stronger part of the field. Paramagnetic substances contain unpaired electrons. Diamagnetic substances are repelled by an external magnetic field, that is, they tend to move away from the stronger part to the weaker part of the field. In diamagnetic substances, all the electrons are paired.
The magnetic moment of a substance arises from the spin angular momentum and the orbital angular momentum of its electrons. In many compounds of the 3d series metals, the orbital contribution is neglected, because the orbital motion of these electrons is quenched by the surrounding species in the compound or solution. The magnetic moment is then calculated by the spin-only formula, in Bohr magnetons (BM):
\[\mu_s = \sqrt{n(n + 2)}\ \text{BM}\]
where n is the number of unpaired electrons.
Consider the following statements about the magnetic behaviour of substances.
(A) Ferromagnetism is an extreme form of paramagnetism.
(B) The green manganate ion is paramagnetic, whereas the permanganate ion is diamagnetic.
(C) Many of the transition metal ions are diamagnetic.
(D) Potassium permanganate shows diamagnetism along with a temperature-dependent weak paramagnetism.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B) and (D) only
A paramagnetic substance is attracted by a magnetic field because it has unpaired electrons; a diamagnetic substance, with all its electrons paired, is repelled.
(A) Ferromagnetism is an extreme form of paramagnetism. — True. Substances that are attracted very strongly by a magnetic field are called ferromagnetic; they are the extreme case of paramagnetic substances.
(B) The green manganate ion is paramagnetic, whereas the permanganate ion is diamagnetic. — True. In MnO42−, Mn is +6 (3d1) with one unpaired electron; in MnO4−, Mn is +7 (3d0) with no unpaired electron.
(C) Many of the transition metal ions are diamagnetic. — False. Many transition metal ions have partly filled d orbitals with unpaired electrons, so they are paramagnetic.
(D) Potassium permanganate shows diamagnetism along with a temperature-dependent weak paramagnetism. — True. This, together with its intense colour, is a property of KMnO4 that is explained by molecular orbital theory.
NCERT (2026-27 edition):
4.3.9 Magnetic Properties – “…Diamagnetic substances are repelled by the applied field while the paramagnetic substances are attracted. Substances which are attracted very strongly are said to be ferromagnetic. In fact, ferromagnetism is an extreme form of paramagnetism. Many of the transition metal ions are paramagnetic.”
4.4.1 Oxides and Oxoanions of Metals – “It has two physical properties of considerable interest: its intense colour and its diamagnetism along with temperature-dependent weak paramagnetism. These can be explained by the use of molecular orbital theory which is beyond the present scope.”
“The manganate and permanganate ions are tetrahedral; the π- bonding takes place by overlap of p orbitals of oxygen with d orbitals of manganese. The green manganate is paramagnetic because of one unpaired electron but the permanganate is diamagnetic due to the absence of unpaired electron.”