A media converter is a device that allows you to interconnect different types of network media, such as copper, fiber, and coaxial cables.
A media converter can be used to connect newer network technologies, such as Gigabit Ethernet or ATM, to existing networks, such as 10BASE-T or 100BASE-T.
A media converter can also be used to extend the distance and improve the immunity of network signals by converting them from electrical to optical or vice versa.
A proxy server, an industrial control system, and a load balancer are not devices that can connect different physical characteristics of network media. They have different functions and purposes in a network.
A proxy server is a device that acts as an intermediary between a client and a server, providing security, caching, and filtering services.
An industrial control system is a system that monitors and controls industrial processes, such as manufacturing, power generation, and transportation.
A load balancer is a device that distributes network traffic across multiple servers, improving performance and availability. Reference:
Media Converters - CompTIA Network+ N10-006 - 1.5
Transceivers (Media Converters) | Network+ Exam Cram: Networking Devices in Modern Networks