During exhalation, the ribs move downwards. The movement of the ribs during exhalation is important for reducing the volume in the thoracic cavity, which helps in pushing the air out of the lungs. The downward movement of the ribs is facilitated by the contraction of the internal intercostal muscles, which assists in decreasing the space between the ribs. As the space between the ribs decreases, the ribcage becomes smaller, leading to a decrease in the volume of the thoracic cavity. This decrease in volume creates an increased pressure in the lungs, forcing air to be expelled. This downward movement of the ribs is an essential part of the breathing process and allows for efficient exhalation.

Alert - correct answer should be 4: The ribs do not move at all during exhalation.