Case: Read the passage and answer the question.
The magnetic susceptibility of a substance is a measure of how readily it responds to an external magnetic field. It gives a measure of the ability of a substance to acquire magnetism. It has no units. Mathematically, it is defined as the ratio of the magnetisation to the magnetic intensity. The susceptibility of a certain substance is \( 2.3\times10^{-5} \).
Which of the following could be the substance described in the passage?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Aluminium
The susceptibility of the substance is small and positive. A material with such a value is paramagnetic.
Option (1) Bismuth — Incorrect. Bismuth is diamagnetic. Its susceptibility is negative.
Option (2) Aluminium — Correct. Aluminium is a paramagnetic material, with a small positive \( \chi \) like the given value.
Option (3) Nickel — Incorrect. Nickel is ferromagnetic. Its susceptibility is large, far above \( 2.7\times10^{-5} \).
Option (4) Water — Incorrect. Water is diamagnetic, so its \( \chi \) has a negative sign.
NCERT (2026-27):
Magnetisation and Magnetic Intensity – “… χ is small and positive for materials, which are called paramagnetic. …”
Paramagnetism – “Some paramagnetic materials are aluminium, sodium, calcium, oxygen (at STP) and copper chloride. …”