Q. Consider the following statements regarding bones in the human body:

1. They consist of 80% solid matter and20% water.
2. Solid matter in the bones is made mainly of cartilage.
3. Impregnation of salts including carbonates and phosphates of lime imparts hardness to the bones.
4. In old age, the proportion of lime decreases and bones become brittle and break easily.

Of these statements:
Answer: 1, 2, 3 and 4 are correct
Notes: All of them are correct.
Bones consist of living cells embedded in a mineralized organic matrix. This matrix consists of organic components, mainly type I collagen – "organic" referring to materials produced as a result of the human body – and inorganic components, primarily hydroxyapatite and other salts of calcium and phosphate.