The correct answer is (c). Vitamin B12 contains cobalt.
Vitamin B12 is a water-soluble vitamin that is essential for human health. It is involved in the production of red blood cells, the function of the nervous system, and the metabolism of proteins, fats, and carbohydrates. Vitamin B12 is found in animal products such as meat, fish, poultry, eggs, and dairy products. It is also found in some fortified foods such as breakfast cereals and nutritional yeast.
Cobalt is a trace element that is essential for the production of vitamin B12. It is found in small amounts in animal products and some plant-based foods. Cobalt is also added to some foods as a supplement.
Iron, nickel, and magnesium are not essential for the production of vitamin B12. They are found in many foods, but they do not have a role in the production of this vitamin.