Area enclosed by curve represents energy lost. If the area of hysteresis loop is less energy loss is low whereas if the area of hysteresis loop is large energy loss is high.

The curie temperature or curie point of a ferromagnetic material is the temperature above which it looses its characteristic ferromagnetic ability to possess a net magnetization in the absence of an external magnetic field. Hence, above curie temperature material is purely paramagnetic.

Magnetic substance when kept in a magnetic field is feebly repelled or thrown out if the substance is diamagnetic.

Therefore,


Or

The materials for a permanent magnet should have high retentivity (so that the magnet is strong) and high coercivity (so that the magnetism is not wiped out by stray magnetic fields). As the material in this case is never put to cyclic changes of magnetization, hence hysteresis is immaterial.

Diamagnetic materials have negative susceptibility. Thus, (c) is wrongly stated.

For permanent magnet we prefer a material with high retentivity (so as to make a stronger magnet) and high coercivity (so that magnetization may not be wiped out easily). For electromagnet we prefer high saturated magnetism, low coercivity and least possible area of hysteresis loop so that electromagnet develops high magnetization, is easily demagnetized and energy loss in a magnetization cycle is least. Therefore, Pis suitable for making permanent magnet and Q for making electromagnet.

Iron is a ferromagnetic substance and ferromagnetic substance obeys Curie-Weiss law above its Curie temperature.