______and ______pairs of ribs are called floating ribs.

Hint: Ribs are present in the thoracic cavity. They are actually long curved bones and form the rib cage. Ribs are attached ventrally to the sternum and dorsally to the vertebral column.

Complete answer: In humans, there is the presence of 12 pairs of ribs. The 1st to 7th pairs of ribs are known as true ribs. True ribs are those ribs that are attached anteriorly to the sternum (chest bone) and posteriorly to the vertebral column. 8th, 9th and 10th pair of ribs are known as false ribs as they are attached anteriorly to the 7th pair of the rib, not to the sternum and posteriorly to the vertebrae. 11th and 12th pairs of ribs are called floating ribs as they are attached only posterior to the vertebrae and the other end is floated. Ribs are located in the front centre of the chest. The diaphragm is a muscular organ present between the ribs, beneath the lungs and regulates breathing. When the air goes in or during inhalation diaphragm moves up and contracts, while exhalation diagram regains its dome shape and relaxes. The liver too is protected by the rib cage but partially. The liver is the largest organ of the body.

Note: Ribs are considered in the axial skeleton. The rib cage protects the delicate internal organs like the heart and lungs. It allows the lungs to expand while breathing. The first pair of the rib is comparatively shorter and wider than other ribs.