What component insulates the inner conductor of coaxial cable from the outer conductor?

The correct answer is the dielectric, which is the material specifically designed to insulate the inner conductor of a coaxial cable from the outer conductor. In coaxial cable construction, the dielectric is integral in ensuring that the electromagnetic signals can travel along the inner conductor without interference from the outer conductor. It also plays a crucial role in maintaining the impedance of the cable, which is essential for preventing signal loss and reflections.

Each of the other options serves different purposes or may not provide adequate insulation. The metal sheath, for example, primarily serves as a protective layer to shield the cable from physical damage and external electromagnetic interference, but it does not provide insulation for the inner conductor. Insulating tape could potentially provide temporary insulation but is not a standard or effective long-term solution for coaxial cable construction. The plastic casing might offer some level of protection or minor insulation but again does not fulfill the specific role of a dielectric in coaxial cable. Therefore, the dielectric is the correct component for insulating the inner conductor.