What happens to a intake and exhaust valve during the power stage cycle in four gas engine?

Intake Valve: During the power stage, the intake valve remains closed. As the piston moves upwards during the compression stroke, the pressure inside the cylinder increases. The intake valve remains closed to prevent any backflow of the compressed air-fuel mixture into the intake manifold.

Exhaust Valve: During the power stroke, the exhaust valve remains closed until the piston reaches the top of the cylinder. As the piston moves down during the power stroke, the pressure of the combusted fuel mixture decreases, and the piston exerts force on the crankshaft. At the appropriate moment, the exhaust valve opens, allowing the hot exhaust gases to escape from the cylinder. This releases the pressure built up during combustion and creates space for the fresh air-fuel mixture to enter the cylinder during the next intake stroke.