Which of the following components is essential for a complete ignition system?

The spark plug is essential for a complete ignition system as it is responsible for igniting the fuel-air mixture within the engine's combustion chamber. When the ignition system receives a signal from the ignition coil, the spark plug generates a high-voltage electrical spark that ignites the compressed mixture, leading to a controlled explosion that powers the engine. Without a functioning spark plug, the ignition system cannot initiate combustion, rendering the engine inoperative.

The other components listed, while important for the overall function of the engine, do not directly relate to the ignition process. The carburetor manages the air-fuel mixture for the engine, the fuel tank stores the fuel, and the exhaust system channels away combustion gases. However, none of these components create the spark necessary to ignite the mixture, which makes the spark plug the fundamental part of the ignition system.