Magnet which is formed naturally is called natural magnet. Man- made magnets are called artificial magnet. For instance,  Bar magnet, U-shaped magnet, etc.

The molecules of the magnetic substance retain the magnetic property. They are known as molecular magnets.

If molecular magnets align in a row, then the substance exhibits magnetic property. If they are kept haphazardly, they do not exhibit magnetic property. This is the molecular theory of magnetism.
Two poles of a magnet are of equal strength because the number of free north poles at one end is equal to the number of free south poles at the other end.

The poles of a magnet cannot be separated even by breaking into pieces because they exist in a pair, every molecule of a magnet has poles in a pair.

A magnet has molecules aligned in the same direction which provides it the magnetic property.

Though an iron is made up of molecular magnets, it does not have magnetic property because the molecules of iron are not aligned in the same direction and until the molecules are not arranged in the same direction, substance does not get magnetic property.

The molecular magnets are arranged in an open chain so that the north pole or the south pole of the molecular magnets lie in the same direction which gives strong force at the poles whereas two opposite poles are arranged at the middle and the force cancel each other. So, poles have more force than the middle portion.

It is because the molecules of the magnetic substance are not in the same direction.

Molecular magnets of magnetic substance are laid in same direction or open chain.