Which term describes the ability of a material to create an opposing magnetic field in response to an external magnetic field?

The concept being described is known as magnetic susceptibility. This term refers to a material's ability to become magnetized when exposed to an external magnetic field. Specifically, susceptibility measures how susceptible a material is to being magnetized and how strong that magnetization will be in response to the applied field.

When a material exhibits susceptibility, it generates an opposing magnetic field when influenced by an external magnetic force. This means that the material will alter the overall magnetic field strength in its vicinity, which is key in various applications, including electromagnetism and material science.

The other terms mentioned are related but describe different properties. Permeability refers to how easily a magnetic field can pass through a material, while magnetic reluctance is a measure of the opposition a material presents to magnetic field lines—essentially the inverse of permeability. Electrical conductivity, on the other hand, relates to a material's ability to conduct electric current and doesn't directly pertain to magnetism. Understanding these distinctions is vital for interpreting materials' behavior in magnetic fields and their applications in various engineering and technological contexts.