Teeth and bones acquire strength and rigidity primarily from calcium. Calcium is an essential mineral that plays a vital role in the development and maintenance of bone and dental health. It is incorporated into the crystal structure of bones and teeth, contributing to their hardness and strength. Calcium also plays a key role in muscle contraction, nerve function, and blood clotting. Fluorine, chlorine, and sodium are not primarily responsible for the strength and rigidity of teeth and bones. Fluorine is known for its role in preventing tooth decay, but it does not directly contribute to their strength. Chlorine is involved in maintaining fluid balance in the body and sodium plays a role in regulating blood pressure and fluid balance but neither directly contribute to the strength and rigidity of teeth and bones.