Correct Answer - Option 1 : More than atmospheric pressure
Concept:
The pressure differential across the intake valves of a naturally aspirated engine is less than one atmosphere, while the pressure differential across the exhaust valves during blowdown can be as high as three or four atmospheres.
The higher pressures near exhaust valves assist the exhaust gases to escape from the combustion chamber. With a small space, they can easily go out of exhaust valve.
Due to these differences in pressure difference during intake and exhaust, it is tougher to induct the air than to exhaust the burnt gases and therefore the intake valve hole has to be bigger than the exhaust valve hole.
