The relation $H \propto I$ and the susceptibility $\chi = \frac{I}{H}$ are not applicable for which of the following substances?

When a magnetic substance is heated,then it

Magnets cannot be made from which of the following substances?

Given below are two statements; one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Electromagnets are made of soft iron.
Reason $R:$ Soft iron has high permeability and low retentivity.
In the light of the above statements,choose the most appropriate answer from the options given below.

Consider the following two statements $A$ and $B$ and identify the correct choice in the given answers.
$A$. Paramagnetism is explained by domain theory.
$B$. Susceptibility of a diamagnetic substance is independent of temperature.

For two types of magnetic materials $A$ and $B$, the variation of $\frac{1}{\chi}$ ($\chi$: magnetic susceptibility) versus temperature $T$ is shown in the figure. Then: