Which flight condition is most likely to cause a stall?

A stall occurs when an aircraft's wing exceeds its critical angle of attack, leading to a significant loss of lift. The flight condition most likely to cause a stall involves flying at low speeds while maintaining a high angle of attack. At low speeds, the airflow over the wings is less energetic, which means that any increase in angle of attack can quickly lead to a point where the airflow begins to separate from the wing surface. This separation drastically reduces the lift generated by the wing.

When pilots fly at low speeds with a high angle of attack, they are operating near the stall margins, making it crucial to manage both speed and angle of attack to avoid entering a stall condition. In contrast, the other conditions listed, such as flying at high speed with a low angle of attack or climbing steadily at an optimal angle, maintain airflow over the wings and keep the aircraft within the safe operating limits, thus reducing the likelihood of a stall. Similarly, descending with reduced power does not inherently create conditions favorable to stalling if managed correctly, especially when maintaining appropriate airspeed and angle of attack.