Correct Option: A

Vitamin B₁₂, vitamin B₁₂ or vitamin B₁₂, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins. It is normally involved in the metabolism of every cell of the human body, especially affecting DNA synthesis and regulation, but also fatty acid synthesis and energy production. Vitamin B₁₂ consists of a class of chemically related compounds (vitamers), all of which have vitamin activity. It contains the biochemically rare element cobalt.