Core of electromagnets are made of ferromagnetic material which has

Ferromagnetic materials have . . . . . . permeability and . . . . . . retentivity.

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.

The variation of the intensity of magnetisation $(I)$ with respect to the magnetising field $(H)$ in a diamagnetic substance is well described by the graph

For a paramagnetic substance, the magnetic susceptibility is

Curie temperature is the temperature above which