Final answer:
A check valve is the device that prevents backflow when a hose is connected to a faucet.
Step-by-step explanation:
The device that prevents backflow when a hose is connected to a faucet is called a check valve.
Check valves allow the flow of water in only one direction, preventing any reverse flow. They are typically installed in plumbing systems, including hose connections to faucets, to prevent water from flowing back into the source.
Check valves work by using a mechanism, such as a spring or a swinging disc, that only allows water to flow in one direction. When the pressure on the inlet side is higher than the outlet side, the valve opens and water can flow through. However, if the pressure on the inlet side becomes lower than the outlet side, the valve closes and prevents any backflow.