Core of electromagnets are made of ferromagnetic material which has

The magnetic susceptibility of a paramagnetic substance at $-173^{\circ} C$ is $1.5 \times 10^{-2}$. To have the susceptibility $0.5 \times 10^{-2}$,the change in temperature in ${ }^{\circ} C$ is

$A$ paramagnetic material has $10^{28} \text{ atoms/m}^3$. Its magnetic susceptibility at temperature $350 \text{ K}$ is $2.8 \times 10^{-4}$. Its susceptibility at $300 \text{ K}$ is

The susceptibility of tungsten is $6.8 \times 10^{-5}$ at temperature $300 \ K$. The susceptibility at temperature $400 \ K$ is

The variation of magnetic susceptibility $(\chi)$ with temperature $(T)$ for a diamagnetic substance is shown correctly by which graph?

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.