Question

Which element provides strength to the exoskeletons of clams and oysters?

Answer 1

chitin

Answer 2

It is the conchiolin, a complex protein secreted by the mantle of some molluscs (clams and oysters).
These proteins are part of a matrix of organic macromolecules that assembled together form the microenvironment where crystals nucleate and grow. This organic matrix also holds and binds to the crystals of aragonite which give such shells their stiffness.

Answer 3

@emiliovega is correct in that molluscs secrete an organic matrix that nucleates and bind aragonite, however the question asks which element (like on the periodic table) provides strength to the exoskeleton. So I'm going to go ahead and say the simple answer to this question is Calcium, as aragonite is a crystal of calcium carbonate. Also @http_yash chitin is a good guess, but it is primarily found in the exoskeletons of insects (which do not contain calcium crystals), and the cell walls of fungi.

Answer 4

good and thanks sdiam45883....