Calcium.
Step-by-step explanation:
The bones along with the cartilage form the skeletal system of the body. The bones are made up of cells called osteocytes. The osteocytes are bound in a hard matrix made of calcium and phosphate salts.
More calcium ion is added more and more mineral salt is formed increasing the hardness of the bone thus making them stronger.
Hence we conclude that, the divalent cation required to create additional bone matrix support is calcium ion.