When a magnetic substance is heated,then it

If $\chi$ stands for the magnetic susceptibility of a substance,$\mu$ for its magnetic permeability,and $\mu_0$ for the permeability of free space,then which of the following is correct?

Curie temperature is the temperature above which

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.

Relative permittivity and permeability of a material are $\varepsilon_r$ and $\mu_r$ respectively. Which of the following values of these quantities are allowed for a diamagnetic material?

$A$ sample of paramagnetic salt contains $2 \times 10^{24}$ atomic dipoles each of dipole moment $1.5 \times 10^{-23} \text{ J T}^{-1}$. The sample is placed under a homogeneous magnetic field of $0.6 \text{ T}$ and cooled to a temperature of $4.2 \text{ K}$. The degree of magnetic saturation achieved is $20 \%$. What is the total dipole moment of the sample for a magnetic field of $0.9 \text{ T}$ and a temperature of $2.8 \text{ K}$ (in $\text{ J T}^{-1}$)?