Final answer:
OPTION D.The state when a magnetic material's molecules are fully aligned and cannot further increase in magnetic field strength with additional current is known as saturation.
Step-by-step explanation:
When a magnetic material's molecules are all lined up, and increases in current flow no longer cause increases in magnetic field strength, the material has reached saturation. This state occurs when the magnetic dipoles within a material are fully aligned with an external magnetic field.
Beyond this point, no additional magnetic field strength can be achieved with an increase in the applied current. In ferromagnetic materials, such as iron, cobalt, nickel, and gadolinium, saturation denotes that the material has reached its maximum magnetization. In this state, the magnetic susceptibility of the material is maximized, and further increases in the external magnetic field will not enhance the magnetization of the material.