Three of the following pairs of the human skeletal parts are correctly matched with their respective inclusive skeletal category and one pair is not matched. Identify the non-matching pair.

The clavicle (collar bone) and the scapula form the pectoral girdle; the glenoid cavity is the depression of the scapula that articulates with the head of the humerus to form the shoulder joint.
So the clavicle and glenoid cavity belong to the pectoral girdle, not the pelvic girdle. (The pelvic girdle is made of the coxal bones and has the acetabulum.)
Humerus and ulna are bones of the fore limb, which is part of the appendicular skeleton (correct).
Malleus, incus and stapes are the three ear ossicles (correct).
The sternum and ribs, with the skull and vertebral column, form the axial skeleton (correct).
Hence the non-matching pair is clavicle and glenoid cavity – pelvic girdle.