In this example question, it says what happens to the pressure if the same amount of gas molecules is transferred from a 5 liter container to a 10 liter container. Remember, pressure equals p=FA. They're saying it's the same amount of gas molecules.
Since it's the same amount of gas molecules, they should exert the same type of force. But what's happening? We're going from a 5 liter container to a 10 liter container, so our area is going up. The size inside the container is increasing.
If force is sustained the same but area is increasing, that's going to cause my pressure to decrease. So here our best option would have to be option B where it's going to decrease.