Given below are two statements:
Statement I: For diamagnetic substance $$-1 \leq x < 0$$, where x is the magnetic susceptibility.
Statement II: Diamagnetic substance when placed in an external magnetic field, tend to move from stronger to weaker part of the field. In the light of the above statements, choose the correct answer from the options give below.

The magnetisation of a linear magnetic medium is given by $$\mathbf{M} = \chi \mathbf{H}$$, where $$\chi$$ is the (volume) magnetic susceptibility and $$\mathbf{H}$$ is the magnetising field.

Relative permeability is defined as $$\mu_r = 1 + \chi$$ $$-(1)$$

Case 1 → Statement I
For a diamagnetic substance:
  • The induced dipoles are opposite to the applied field, hence $$\chi$$ is negative.
  • In naturally occurring materials $$|\chi|$$ is very small (of the order $$10^{-5}$$).
  • Condition $$\mu_r \gt 0$$ must hold for ordinary matter. From $$(1)$$ this gives
    $$1 + \chi \gt 0 \;\;\Longrightarrow\;\; \chi \gt -1$$

Combining the facts “$$\chi$$ is negative” and “$$\chi \gt -1$$” we obtain the range
$$-1 \le \chi \lt 0$$

Therefore Statement I is correct.

Case 2 → Statement II
The potential energy of a small sample in a non-uniform field is $$U = -\tfrac{1}{2}\,\chi V \mu_0 H^2$$, where $$V$$ is its volume. For a diamagnet $$\chi \lt 0$$, so $$U$$ increases with $$H^2$$. To minimise energy the sample drifts toward the region where $$H$$ is smaller, that is, from the stronger part of the field to the weaker part.

Hence Statement II is also correct.

Since both statements are true, the correct choice is Option D.