(a) Ball and socket joint is a movable joint. In this, a bone with a round head fits into the hollow space of another bone.
This makes the bone to rotate freely. For example, bones of the hip and shoulder can move in all directions due to ball and socket joints.
(b) The lower jaw bone of the skull is the only movable bone. It allows us to chew food and talk. It is known as mandible.
(c) Our elbow cannot move backwards because it has hinge joints that only allow back and forth movement and movement in one plane only.