Final answer:
Option 3, the mandible, is the largest bone of the facial skeleton that makes up the lower jaw. It is the only movable bone of the skull and plays a vital role in mastication and facial expressions.
Step-by-step explanation:
The bone that constitutes the lower jaw and holds the distinction of being the largest bone within the facial skeleton is the mandible.
The facial bones, including the mandible, support various facial structures and are crucial for functions such as mastication (chewing) and communication. The mandible's unique feature is that it is the only movable bone of the skull, allowing the mouth to open and close. In the human skull, there are 14 facial bones, among which the maxilla forms the upper jaw, while the zygomatic bones, also known as cheekbones, and nasal bones have their distinctive roles, none of which include forming the lower jaw like the mandible does.
At birth, the mandible consists of two halves which fuse together to form the single U-shaped bone that is critical for dental support and provides attachment points for the facial muscles.