The correct answer is: B. Cobalt
Vitamin B12 is a water-soluble vitamin that is essential for human health. It is involved in many important bodily functions, including the production of red blood cells, the maintenance of nerve function, and the metabolism of carbohydrates, fats, and proteins.
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.
Vitamin B12 deficiency can cause a variety of symptoms, including fatigue, weakness, pale skin, shortness of breath, and loss of appetite. In severe cases, it can lead to nerve damage, anemia, and even death.
Cobalt is the metal ion that is essential for the formation of vitamin B12. It is found in the center of the vitamin’s molecule, and it is necessary for the vitamin to be active.
Nickel, iron, and zinc are also metal ions, but they are not essential for the formation of vitamin B12. They may play a role in the absorption and metabolism of the vitamin, but they are not required for its production.
In conclusion, the metal ion present in vitamin B12 is cobalt.