Which one of the following is not a ferromagnetic material?
- (a)Cobalt
- (b)Iron
- (c)Silver
- (d)Ferric chloride
UPSC cancelled this question — the official key records no correct option for it, and marks were not awarded on any answer. The reason is visible in the options themselves. The stem asks which material is NOT ferromagnetic, and two of the four qualify. Silver is diamagnetic and ferric chloride is paramagnetic, so neither is ferromagnetic; meanwhile cobalt and iron are the two textbook ferromagnets. A negative stem that admits two defensible answers cannot be marked, which is why it was dropped. Treat this item as a concept lesson on the classes of magnetic material rather than as a question with an answer, and do not let an answer key you find elsewhere persuade you that one of the two was 'more correct'.
- (a)Cobalt — Not an answer to the stem, because cobalt IS ferromagnetic. It is one of the three ferromagnetic elements at room temperature, alongside iron and nickel, with a Curie temperature of about 1,394 K — the highest of the three.
- (b)Iron — Not an answer either, because iron is the ferromagnet — the element the word is named after, with a Curie temperature of about 1,043 K. Serving 'iron' as the answer to this item would be plainly wrong, and that is exactly the error the cancellation guards against.
- (c)Silver — This is one of the two defensible answers, not a wrong option. Silver has no unpaired electrons in the metal's conduction behaviour and is diamagnetic — weakly repelled by a magnetic field — so it is certainly not ferromagnetic.
- (d)Ferric chloride — This is the other defensible answer. Iron(III) chloride is paramagnetic: the Fe(III) centre is high-spin d5 with five unpaired electrons, giving a large positive molar susceptibility. Paramagnetic is not ferromagnetic, so this option also satisfies the stem — and two satisfied options are what made the item unkeyable.
Materials are sorted by how they respond to an applied magnetic field. Diamagnetic substances have no unpaired electron spins and are weakly repelled by a field; silver, copper, water and bismuth behave this way. Paramagnetic substances have unpaired spins that align with an applied field but lose that alignment as soon as the field is removed, because thermal motion randomises them; ferric chloride, oxygen gas and aluminium are examples. Ferromagnetic substances are the special case in which neighbouring spins couple to one another and align spontaneously in domains, so the material stays magnetised after the field is removed — only iron, cobalt, nickel, gadolinium and their alloys do this at or near room temperature, and each loses the property above its Curie temperature.
The trap the paper walked into is the difference between an element and its compound. A candidate who reasons 'ferric chloride contains iron, and iron is ferromagnetic' will call ferric chloride ferromagnetic and pick silver; a candidate who knows that magnetic ordering is a property of the bulk lattice, not of the element in it, will see that ferric chloride is merely paramagnetic and may pick either. Both readings end at a genuinely non-ferromagnetic material, which is why the item cannot be marked. The chemistry is worth carrying away: in iron(III) chloride the iron centres are far apart and coupled only weakly, so their five unpaired d electrons respond to a field individually rather than locking together into domains, and the compound is paramagnetic. UPSC dropped four items across the CDS papers of 2021 to 2024 for exactly this kind of double-answer defect.
- The common ferromagnetic materials are the metals iron, cobalt and nickel, most of their alloys, and certain rare-earth metals such as gadolinium.
- All forms of ferric chloride are paramagnetic, because the high-spin Fe(III) centre carries five unpaired 3d electrons.
- Silver is diamagnetic — weakly repelled by a magnetic field, with no permanent magnetic moment.
- A ferromagnet loses its spontaneous magnetisation above its Curie temperature — about 1,043 K for iron and about 1,394 K for cobalt.
Two of the four options are genuinely non-ferromagnetic, which is precisely why this question has no answer.
- Assuming any iron compound must be ferromagnetic; magnetic ordering is a property of the lattice, not of the element present in it.
- Treating paramagnetic and ferromagnetic as the same thing — a paramagnet keeps no magnetisation once the field is removed.
- Accepting a solution elsewhere that names one answer to this item; UPSC recorded no correct option for it.
Asked as a one-line negative-stem item on magnetic classes. The paper's own option set contained two valid answers, and UPSC dropped the question rather than key one of them.
Which one of the following is paramagnetic in nature?
- (a) Iron
- (b) Hydrogen
- (c) Oxygen
- (d) Nitrogen
Answer(c) Oxygen — molecular oxygen has two unpaired electrons in its antibonding orbitals; hydrogen and nitrogen are diamagnetic and bulk iron is ferromagnetic.
The same three-way classification asked cleanly, with only one option in the class named. It is the model of how this content can be examined without ambiguity, and its own distractor (a) records that bulk iron is ferromagnetic rather than paramagnetic.
- practice — not a real PYQ
Which one of the following is diamagnetic?
- (a)Cobalt
- (b)Nickel
- (c)Silver
- (d)Gadolinium
Answer(c) Silver — it is weakly repelled by a magnetic field, while the other three are ferromagnetic at or near room temperature.
- practice — not a real PYQ
Above its Curie temperature, a ferromagnetic material becomes
- (a)diamagnetic
- (b)paramagnetic
- (c)more strongly ferromagnetic
- (d)non-magnetic in every sense
Answer(b) paramagnetic — thermal agitation destroys the domain alignment, leaving only the weak field-induced response of a paramagnet.