Which control surface is primarily used to adjust the pitch of the aircraft?

The elevator is the primary control surface used to adjust the pitch of an aircraft. Located at the tail of the aircraft on the horizontal stabilizer, it works by changing the airflow over its surface as the pilot moves the control yoke or stick. When the elevator is deflected upward, it increases lift at the tail, causing the nose of the aircraft to pitch down. Conversely, when the elevator is pushed downward, it decreases lift at the tail, causing the nose to pitch up. This direct connection between the position of the elevator and the aircraft's nose attitude makes it the key control surface for managing the pitch attitude during flight.

In contrast, ailerons are primarily responsible for controlling roll, rudders are for yaw, and flaps are used to increase lift and drag during takeoff and landing rather than directly altering pitch. Each of these other control surfaces has its own specific function which complements the overall aerodynamic control of the aircraft, but they do not directly affect the pitch.