Needles $N_1, N_2$ and $N_3$ are made of a ferromagnetic,a paramagnetic and a diamagnetic substance respectively. $A$ magnet when brought close to them will

Pick out the $WRONG$ statements about magnetic substances ($\chi = \text{magnetic susceptibility}$, $\mu_r = \text{relative permeability}$).
$I$. Substances with $-1 \le \chi < 0$ are diamagnetic
$II$. Substances with $\chi \gg 1$ are paramagnetic
$III$. Substances with $\chi \ll 1$ are ferromagnetic
$IV$. Substances with $\mu_r \gg 1$ are ferromagnetic

What materials should be used to make permanent magnets?

Explain diamagnetism and diamagnetic substances.

From a molecular viewpoint,discuss the temperature dependence of susceptibility for diamagnetism,paramagnetism,and ferromagnetism.

The magnetic susceptibility of an ideal diamagnetic substance is