On applying an external magnetic field to a ferromagnetic substance,the domains:

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

Statement $I :$ The ferromagnetic property depends on temperature. At high temperature,a ferromagnet becomes a paramagnet.
Statement $II :$ At high temperature,the domain wall area of a ferromagnetic substance increases.
In the light of the above statements,choose the most appropriate answer from the options given below :

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

Why is steel suitable for making permanent magnets?

$A$ superconductor exhibits perfect