Which of the following is NOT a transmission medium?

The reason the correct answer is that a router is not a transmission medium lies in the definitions of the terms involved. Transmission media refer to the physical pathways through which data is transmitted from one point to another. These media facilitate the transfer of signals and data, allowing communication to occur.

Copper and fiber optic cables are classic examples of transmission media. Copper cables transmit data using electrical signals, while fiber optic cables use light signals to transfer data over long distances with high speed and minimal loss. Both of these serve as the actual conduits for data transmission.

Microwave, while somewhat different in its technology, is also classified under transmission media. Microwaves are used in wireless communication and can transmit data over the air, utilizing radio wavelengths.

In contrast, a router is a networking device that manages traffic between different networks. Its primary function is to direct data packets between devices on a network but does not itself transmit signals or data over a physical medium. Therefore, it does not meet the criteria to be classified as a transmission medium.