During a stall, the lift decreases and drag increases primarily due to the disrupted airflow over the wings of the aircraft.

Decrease in Lift: Lift is generated by the pressure difference between the upper and lower surfaces of the wings. At normal flight conditions, the air flows smoothly over the wings, creating this pressure difference and generating lift. However, during a stall, the angle of attack (the angle between the chord line of the wing and the direction of the airflow) becomes too high. This disrupts the smooth flow of air over the wings, causing separation of airflow and a decrease in lift generation. Essentially, the wing loses its ability to provide the necessary lift to keep the aircraft airborne.

Increase in Drag: Drag is the force that opposes the motion of the aircraft through the air. During a stall, as the angle of attack increases beyond the critical angle, the airflow over the wings becomes turbulent, leading to an increase in drag. This increase in drag further exacerbates the stall condition by slowing down the aircraft's forward speed. The disrupted airflow also contributes to the creation of additional forms of drag, such as induced drag, which further hampers the aircraft's performance.