The Curie-Weiss law is obeyed by iron at a temperature ......

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.

Magnetic shielding is done by surrounding the instrument to be protected from magnetic field by

$A$ paramagnetic substance is placed in a non-uniform magnetic field, then

Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature,then it will show

The most exotic diamagnetic materials are