What occurs just before the compression stroke ends?

The correct answer is that just before the compression stroke ends, a high voltage arc ignites the mixture. In a four-stroke internal combustion engine, the compression stroke occurs after the intake stroke and before the power stroke. During the compression stroke, the piston moves upward, compressing the air-fuel mixture within the cylinder. This compression increases the temperature and pressure of the mixture, making it more volatile.

When the piston is close to its highest position, a spark plug provides a high voltage arc that ignites the compressed air-fuel mixture. This ignition happens just before the end of the compression stroke, leading to the power stroke where the combustion energy forces the piston downward.

Other choices do not align with the sequence of events in the cycle. The closing of the valves occurs earlier in the cycle, ensuring that the combustion takes place in a sealed part of the cylinder. The piston reaching its lowest point describes the end of the power stroke, not the compression stroke. Filling of the fuel tank is unrelated to the internal events of the engine cycle itself.