What is the name of the pelvic socket into which the femur fits to form the hip joint?

The correct choice is the acetabulum, which is the cup-shaped socket in the pelvis that accommodates the head of the femur. This structure is crucial in the formation of the hip joint, allowing for a ball-and-socket joint that provides a wide range of motion for the leg and stability for weight-bearing activities. The acetabulum is formed by the fusion of three pelvic bones: the ilium, ischium, and pubis. This joint design facilitates activities such as walking, running, and jumping, where the hip joint plays a critical role in mobility and balance.

Other terms do not relate to the hip socket. The acromion is part of the shoulder blade, the appendix is an appendage in the digestive tract, and the aorta is the main artery that carries blood from the heart. Understanding these anatomical structures and their functions is key in fields such as anatomy, medicine, and physical rehabilitation.