The matrices of bones are made up of (a) Calcium and magnesium (b) Magnesium and phosphate (c) Calcium and potassium (d) Calcium and phosphate

The primary components of bone matrix are organic and inorganic materials. The organic part is mostly composed of Type I collagen (about 90%), while the inorganic part is primarily composed of hydroxyapatite, a mineral crystal that provides hardness and rigidity to the bones. Hydroxyapatite is composed of calcium, phosphorus, and oxygen.

Now let's evaluate each of the given options to see which one reflects the right combination of elements found in the matrices of bones: (a) Calcium and magnesium: Calcium is indeed a major component of bone matrix, found in hydroxyapatite. Magnesium is also found in bones, but it is in trace amounts and not part of the main matrix structure. (b) Magnesium and phosphate: Magnesium, as mentioned earlier, is not a major component of bone matrix. Phosphate, on the other hand, is part of the hydroxyapatite crystal, which makes up the inorganic portion of bone matrix. (c) Calcium and potassium: Calcium is a major component of the bone matrix, but potassium is not. Potassium has a crucial role in various biological processes but is not part of the main bone matrix structure. (d) Calcium and phosphate: Calcium is a major component of the bone matrix, and phosphate is part of the hydroxyapatite crystal component that constitutes the inorganic part of the bone matrix.

Based on the evaluation above, the correct combination of elements that makes up the matrices of bones is: (d) Calcium and phosphate