Wireless networks are primarily used to replace which of the following?

Wireless networks primarily serve to replace the physical connection that a patch cord provides between a PC and a wall outlet. When a device is connected to a network via a physical cable, such as an Ethernet patch cord, it relies on that cable to transmit data. With wireless networking, this physical connection is not needed, as the wireless signal carries data between the device and the network access point, allowing for mobility and flexibility in how devices connect to the network.

The other options presented do not represent the primary role of wireless networks. The Ethernet switch, for example, is a vital component that manages data traffic within a wired network but is not something that can be directly replaced by wireless technology. The fiber optic connection refers to high-speed data transmission methods, which wireless cannot fully emulate in terms of speed and reliability. Lastly, a wireless router is instrumental in facilitating the wireless connectivity itself rather than being something wireless networks seek to replace. Instead, it acts as a bridge for devices to connect to wireless networks.