A ferromagnetic substance becomes a permanent magnet when it is placed in a magnetic field because ________.

A ferromagnetic substance is defined as a substance which is strongly attracted by a magnetic field. In the unmagnetised substance, the domains are randomly oriented but when the substance is placed in a magnetic field, the domains are oriented in the direction of the magnetic field. Option (i) is correct.

Diamagnetic substances are those which are weakly repelled by the magnetic field as their domains get oriented in the opposite direction of the magnetic field. Option (ii) is incorrect.

When domains are oriented randomly, there is no net magnetic behavior shown by the substance. All substances have some amount of magnetic properties associated to it and are affected by the magnetic field Option (iii) and (iv) are incorrect.