What is the common name for the sternum?

The sternum is commonly referred to as the breastbone. This flat bone is located in the front of the thoracic cavity and serves as a central point for the ribs to attach, forming part of the rib cage. Its primary function is to protect vital organs located in the chest, such as the heart and lungs. The term "breastbone" is widely understood and used in both medical and lay contexts, making it the correct choice for identifying this specific bone.

The other options do not accurately represent the sternum; the rib cage is a structure that includes the sternum along with the ribs, the spine refers to the vertebral column located at the back, and the collarbone is another name for the clavicle, which is located at the front of the chest but distinct from the sternum itself.