Arrange the following solids in the decreasing order of their magneti…

The correct answer is Option (3) → B > D > C > A

Solids differ in how strongly a magnetic field attracts them: ferromagnetic solids are attracted very strongly, ferrimagnetic solids less strongly (their domain moments cancel only in part), antiferromagnetic solids have no net moment because their domain moments cancel fully, and diamagnetic solids are weakly repelled.

• (B) \( \ce{CrO2} \) — first. It is ferromagnetic, attracted very strongly and can be permanently magnetised.

• (D) \( \ce{Fe3O4} \) — second. Magnetite is ferrimagnetic: domains point both ways in unequal numbers, so a net moment remains, but it is weaker than in a ferromagnetic solid.

• (C) MnO — third. It is antiferromagnetic: equal numbers of opposite domains cancel, so it is hardly attracted.

• (A) NaCl — last. All its electrons are paired, so it is diamagnetic and is weakly repelled by the field.

Shortcut: Options (1) and (3) start with the ferromagnetic \( \ce{CrO2} \) (B); only Option (3) ends with the diamagnetic NaCl (A).

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Magnetic Properties – “… (ii) Diamagnetism: Diamagnetic substances are weakly repelled by a magnetic field. H₂O, NaCl and C₆H₆ are some examples of such substances. They are weakly magnetised in a magnetic field in opposite direction. Diamagnetism is shown by those substances in which all the electrons are paired and there are no unpaired electrons. Pairing of electrons cancels their magnetic moments and they lose their magnetic character.
(iii) Ferromagnetism: A few substances like iron, cobalt, nickel, gadolinium and CrO₂ are attracted very strongly by a magnetic field. Such substances are called ferromagnetic substances. Besides strong attractions, these substances can be permanently magnetised.
(iv) Antiferromagnetism: Substances like MnO showing antiferromagnetism have domain structure similar to ferromagnetic substance, but their domains are oppositely oriented and cancel out each other’s magnetic moment (Fig. 1.32 b).
(v) Ferrimagnetism: Ferrimagnetism is observed when the magnetic moments of the domains in the substance are aligned in parallel and anti-parallel directions in unequal numbers (Fig. 1.32 c). They are weakly attracted by magnetic field as compared to ferromagnetic substances. Fe₃O₄ (magnetite) and ferrites like MgFe₂O₄ and ZnFe₂O₄ are examples of such substances. These substances also lose ferrimagnetism on heating and become paramagnetic.”