Final answer:
The medium that uses an insulator is the fiber-optic cable, which uses plastic or glass fibers to transmit light signals with high efficiency and minimal loss over long distances.B is the correct option.
Step-by-step explanation:
The medium that uses an insulator is a fiber-optic cable. In fiber-optic cables, light signals are transmitted through fibers of plastic or glass, which act as insulators.
The fibers are thin enough that light entering at a certain angle will strike the inside surface at greater than the critical angle, leading to total internal reflection within the fiber. This allows the light to be transmitted over long distances without significant loss.
A key attribute of fiber-optic communication is low loss, high bandwidth, and reduced crosstalk, making it superior for long-distance communications compared to electrical-based systems. Other options such as satellite, coaxial, and twisted pair do not solely rely on insulators for signal transmission; for example, coaxial cables consist of concentric conductors separated by insulation but also require conductive materials for the transmission of electrical signals. Hence, the mentioned correct option in the final answer is fiber-optic.