The correct answer is:
(b) how easily the magnetic flux is set up
Explanation:
Permeability (μ\muμ) is a property of magnetic materials that describes how easily a material can support the formation of a magnetic field within itself. It represents the ability of a material to conduct magnetic flux.
In other words, permeability measures how easily magnetic flux lines can pass through a material when a magnetizing force is applied. The higher the permeability, the easier it is for the material to establish magnetic flux.
Thus, permeability is related to how easily the magnetic flux is set up within the material when exposed to an external magnetic field, which matches option (b).