Explanation: Permeability (symbol μ) is a fundamental property of a material that describes its ability to support the formation of a magnetic field within itself. It quantifies how easily magnetic lines of flux can pass through or be concentrated by a substance. Option B correctly defines permeability as the ratio of the magnetic flux density (B) inside a substance to the magnetizing force (H) that produces it (μ = B/H). This ratio indicates a material's responsiveness to an external magnetic field. Materials with high permeability, like iron cores, are essential in inductors and transformers to concentrate magnetic fields, improving their efficiency and performance in radio frequency circuits. Option A describes an electromagnet, which is a device that creates a magnetic field, rather than defining the property of permeability itself. Option C describes the internal molecular process of magnetization in ferromagnetic materials, which *results* in high permeability, but it is not the formal definition of the permeability ratio.