Pick out the WRONG statements about magnetic substances.
(\(\chi\) = magnetic susceptibility)
(\(\mu_r\) = relative permeability).
I. Substances with \(-1 \leq \chi < 0\) 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.

For diamagnetic substances, the magnetic susceptibility \(\chi\) is small and negative, so \(-1 \leq \chi < 0\). Statement I is correct.

For paramagnetic substances, \(\chi\) is small and positive, so \(0 < \chi < \epsilon\). Statement II states \(\chi \gg 1\), which is incorrect as this condition applies to ferromagnetic substances.

For ferromagnetic substances, \(\chi\) is very large and positive, so \(\chi \gg 1\). Statement III states \(\chi \ll 1\), which is incorrect.

For ferromagnetic substances, the relative permeability \(\mu_r = 1 + \chi\). Since \(\chi \gg 1\), it follows that \(\mu_r \gg 1\). Statement IV is correct.

Therefore, statements II and III are wrong.

Answer: II and III