Magnetic Materials And Susceptibility

NCERT Class 12, Chapter 5 (Magnetism and Matter) classifies magnetic materials by their susceptibility $\chi$, which relates magnetisation to the applied field. Diamagnetic materials have a small negative susceptibility, so they are weakly repelled and tend to move toward weaker field regions; examples include bismuth, copper, and water. Paramagnetic materials have a small positive susceptibility and are weakly attracted, so this option is incorrect for a repelled substance. Ferromagnetic materials such as iron have a very large positive susceptibility and are strongly attracted, contradicting weak repulsion. Ferrimagnetic materials also show net positive magnetisation and attraction, so they too are ruled out. Because the defining features here are 'weakly repelled' and 'negative susceptibility', only diamagnetism fits both. Plausibility check: a negative $\chi$ means the induced magnetisation opposes the applied field, and an opposing magnetisation naturally produces repulsion, so the sign of susceptibility and the observed repulsion are consistent, confirming the diamagnetic classification.