Explanation: Permeability is a fundamental property of a material that describes its ability to support the formation of a magnetic field within itself. **B) The ratio of magnetic flux density in a substance to the magnetizing force which produces it** is the correct definition. It's represented by the Greek letter mu ($\mu$) and is mathematically expressed as $\mu = B/H$, where $B$ is the magnetic flux density (strength of the magnetic field within the material) and $H$ is the magnetizing force (strength of the external magnetic field applied to the material). A higher permeability means the material can concentrate magnetic flux lines more effectively. **A) The magnetic field created by a conductor wound on a laminated core and carrying any electric current** describes an electromagnet or an inductor, not the definition of permeability itself. Permeability is a property *of the core material* used in such a device. **C) Polarized molecular alignment in a ferromagnetic material while under the influence of a magnetizing force** describes the *process* by which ferromagnetic materials become magnetized (their magnetic domains align). While this process is related to a material's permeability, it is not the definition of the property. **D) Both A and C** is incorrect as A and C are individually incorrect.