Answer: The correct answer is "law of poles".
Step-by-step explanation:
Magnetic field lines: These are the area around the magnet in which the magnetic force can be experienced. The strength of the magnetic field is stronger at the poles of the magnet. It decreases from the poles.
The direction of the magnetic field lines is from north pole to south pole.
Law of poles: The same poles of the magnets repel each other with magnetic force of repulsion between the poles.
The opposite poles of the magnets attract each other with the magnetic force of attraction between the poles.
The strength of the magnetic field does not follow an inverse square law. The force from the magnet decreases faster than an inverse square law because all magnets have two opposite poles and single pole does not exist.
Therefore, The strength of a magnetic field follows law of poles.