For a ferromagnetic material, the susceptibility \( (\chi) \) is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( \chi \gg 1 \)
Magnetic susceptibility \( \chi \) measures how strongly a material is magnetised by an applied field (\( M = \chi H \)). In a ferromagnet the atomic moments line up in domains, so even a small field produces a very large magnetisation: \( \chi \) is large and positive (of the order of \( 10^{3} \) or more).
Why the other options are incorrect
Option (1) negative — Incorrect. A small negative \( \chi \) is typical of diamagnetic materials.
Option (2) zero — Incorrect. \( \chi = 0 \) means no magnetisation at all, as in vacuum.
Option (3) \( 0 \lt \chi \lt 1 \) — Incorrect. A small positive \( \chi \) is typical of paramagnetic materials.
NCERT (2026-27):
Magnetic Properties of Materials – “The discussion in the previous section helps us to classify materials as diamagnetic, paramagnetic or ferromagnetic. In terms of the susceptibility \( \chi \), a material is diamagnetic if \( \chi \) is negative, para- if \( \chi \) is positive and small, and ferro- if \( \chi \) is large and positive.”