What device boosts power by increasing the fuel/air mixture delivered to the engine?

The correct choice is a supercharger. This device functions by compressing the air entering the engine, which allows a greater volume of the fuel/air mixture to be delivered. By increasing the density of the air intake, the supercharger boosts the engine's power output without relying on exhaust gases, as it is mechanically driven by the engine itself.

A turbocharger also increases power, but it does so by utilizing exhaust gases to spin a turbine, which then compresses the incoming air. While it achieves a similar end result—enhancing the power of the engine—the mechanism of operation differs significantly from that of a supercharger.

A fuel injector is responsible for delivering the precise amount of fuel into the engine's combustion chamber but does not increase the power on its own by adjusting the fuel/air mixture.

The throttle body controls the amount of air entering the engine based on the driver's input but does not function as a device that specifically boosts power through the addition of more air/fuel mixture.

Understanding these distinctions clarifies why a supercharger is identified as the correct answer for enhancing power through the compression of the fuel/air mixture delivered to the engine.