During which stroke do exhaust gases exit the engine?

The correct choice is the exhaust stroke, during which exhaust gases are expelled from the engine. This stroke is the final phase of the four-stroke cycle in an internal combustion engine. After the power stroke, where fuel and air have been ignited and have caused the piston to move down, the exhaust stroke follows. During this phase, the piston moves back up, creating pressure that forces the spent exhaust gases out of the combustion chamber through the open exhaust valves.

In contrast, the compression stroke is when the mixture of air and fuel is compressed to prepare for ignition, while the intake stroke allows fresh air (and fuel, in gasoline engines) to enter the combustion chamber. The power stroke is the phase where combustion occurs, and it generates the power that moves the piston downwards. Therefore, the exhaust stroke is distinct and critical for clearing the engine of combustion by-products, enabling the cycle to continue efficiently.