Which two bones articulate in the ball and socket joint of the upper arm?

The correct answer is that the humerus and scapula articulate in the ball and socket joint of the upper arm. This joint is known as the glenohumeral joint, where the head of the humerus fits into the shallow cavity of the scapula called the glenoid. This anatomical structure allows for a high degree of mobility, enabling the arm to move freely in various directions, such as flexion, extension, abduction, adduction, and rotation. The design of the ball and socket joint creates a wide range of motion, critical for the functionality of the shoulder.

In contrast, while the clavicle connects to the scapula and plays a role in shoulder movements, it does not form a ball and socket joint with either of the bones listed in the question. The radius is a forearm bone that connects to the humerus at the elbow joint, not in the shoulder area. Lastly, although the clavicle does connect to the humerus through the shoulder, it doesn't participate in a ball and socket arrangement. Hence, the humerus and scapula are the correct pair forming the ball and socket joint in the upper arm.