The correct answer is option 4, Iodine. Iodine is obtained from sea algae. Sea algae, also known as seaweed, is a type of algae that grows in the ocean. It is a rich source of iodine, among other nutrients. Iodine is an essential mineral that is important for the production of thyroid hormones, which regulate the body`s metabolism. It is also used in the production of various pharmaceuticals and industrial chemicals. While options 1, 2, and 3 are elements found in nature, they are not specifically obtained from sea algae. Therefore, they are not correct answers in this context.