Out of 'X' pairs of ribs in humans only 'Y' pairs are true ribs. Select the option that correctly represents values of X and Y and provides their explanation.

In the rib cage, there are 12 pairs of bones. Out of 12, the first 7 pairs are the true ribs as they are directly attached to the sternum and vertebral column. Whereas the last 5 pairs only attach to the vertebral column and indirectly attach to the sternum. Out of 5 pairs, 7 - 10 attached to the costal cartilage and called false ribs, and the last 11th and 12th have no interior attachment and called floating ribs. Thus, the correct answer is option B.