Correct Answer: Calcium carbonate

Solution : The correct answer is Calcium carbonate.

The primary constituent of pearls is calcium carbonate. Pearls are formed within the soft tissue of a living shelled mollusc, such as an oyster or mussel, as a defence mechanism against irritants. The mollusc secretes layers of nacre (mother-of-pearl), primarily composed of calcium carbonate, around the irritant, resulting in the formation of a pearl.