The correct answer is option 1: Vitamin B12. Vitamin B12 is a water-soluble vitamin that is necessary for various functions in the body, such as the production of red blood cells and the functioning of the nervous system. It is also known as cobalamin because it contains the element cobalt. Cobalt is an essential component of the molecular structure of Vitamin B12, and without it, the vitamin cannot carry out its activities in the body. Vitamin D (option 2) is not related to cobalt and is mainly known for its role in bone health. Vitamin B2 (option 3) is also not dependent on cobalt and is involved in energy production and metabolism. Vitamin A (option 4) is not directly related to cobalt and is important for vision, immune function, and cell growth.