“Strength”, whatever it means, comes form inorganic components, totaling about 67% of bone, not a single element. Here is the chemical composition of human bones (%): Ca(II) 39, collagen (protein) 33, PO4(III) 17, CO3(II) 10.
Collagen , it is a protein that provides a soft framework, and calcium phosphate is a mineral that adds strength and hardens the frame work. This combination of collagen and calcium makes the bone strong and flexible enough to withstand stress
