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.

The magnetic susceptibility of a paramagnetic substance is:

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

$A$ sample of paramagnetic salt contains $2.0 \times 10^{24}$ atomic dipoles each of dipole moment $1.5 \times 10^{-23} \; J \, T^{-1}$. The sample is placed under a homogeneous magnetic field of $0.64 \; T$ and cooled to a temperature of $4.2 \; K$. The degree of magnetic saturation achieved is $15 \%$. What is the total dipole moment of the sample for a magnetic field of $0.98 \; T$ and a temperature of $2.8 \; K$? (Assume Curie's law)

Which of the following is most suitable for the core of electromagnets?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$. Consider a ferromagnetic material:
Assertion $(A)$: The individual atoms in a ferromagnetic material possess a magnetic dipole moment and interact with one another in such a way that they spontaneously align themselves forming domains.
Reason $(R)$: At high enough temperature, the domain structure of a ferromagnetic material disintegrates. Thus, magnetization will disappear at a high enough temperature known as the Curie temperature.
In the light of the above statements, choose the correct answer from the options given below: