Answer:

Transmission medium for a computer network exposed to electrical interferences: Optical fiber

Introduction:
In a computer network, the transmission medium is the physical path through which data is transmitted from one device to another. It is crucial to choose the appropriate transmission medium based on various factors, including the presence of electrical interferences. Electrical interferences can disrupt the data transmission process, leading to errors and data loss. In such cases, an optical fiber is the most appropriate transmission medium.

Explanation:
1. Unshielded twisted pair: Unshielded twisted pair (UTP) cables consist of multiple pairs of insulated copper wires twisted together. While UTP cables are commonly used for Ethernet networks, they are susceptible to electrical interferences. Without proper shielding, UTP cables can pick up electromagnetic interference (EMI) and radio frequency interference (RFI) from nearby electrical devices, resulting in data errors and loss.

2. Coaxial cable: Coaxial cables consist of a central conductor surrounded by a layer of insulation, a metallic shield, and an outer protective layer. While coaxial cables provide better protection against electrical interferences compared to UTP cables, they are still susceptible to EMI and RFI. The metallic shield helps reduce interference, but it may not be sufficient in highly electrically noisy environments.

3. Microwave: Microwave transmission involves using radio signals in the microwave frequency range to transmit data wirelessly. While microwave transmission is effective in certain scenarios, it is not the most appropriate choice for a computer network exposed to electrical interferences. Microwave signals can be affected by atmospheric conditions, physical obstacles, and other wireless devices, leading to signal degradation and potential data loss.

4. Optical fiber: Optical fiber is a transmission medium that uses thin strands of glass or plastic to transmit data as pulses of light. It is the most suitable choice for a computer network exposed to electrical interferences due to the following reasons:
- Immunity to electrical interferences: Optical fiber is immune to EMI and RFI since it does not conduct electricity. It is not affected by nearby electrical devices or power lines, ensuring reliable data transmission.
- High bandwidth and low signal degradation: Optical fiber offers high bandwidth, allowing for the transmission of large amounts of data at high speeds. It is also resistant to signal degradation over long distances, ensuring reliable data transmission without the need for repeaters.
- Security: Optical fiber provides enhanced security as it is difficult to tap into or intercept the data being transmitted. Unlike copper-based cables, optical fiber does not emit electromagnetic signals that can be intercepted.

Conclusion:
Considering the susceptibility of other transmission media to electrical interferences, optical fiber is the most appropriate choice for a computer network exposed to such interferences. It offers immunity to EMI and RFI, high bandwidth, low signal degradation, and enhanced security.