Vitamin B₁₂ is

all are correct

The correct answer is option 4.  all are correct.

Let us explore each statement about Vitamin \(B_{12}\) in detail:

1. Vitamin \(B_{12}\) is cyanocobalamin complex

Cyanocobalamin is one form of Vitamin \(B_{12}\), which is a complex organometallic compound. It contains a central cobalt ion \((Co)\) within a corrin ring, which is similar in structure to the porphyrin ring found in heme. In cyanocobalamin, the cobalt ion is coordinated with a cyanide \((CN)\) group, hence the name "cyanocobalamin." Vitamin \(B_{12}\) also exists in other forms, such as methylcobalamin and adenosylcobalamin, where different groups replace the cyanide group.

2. Vitamin \(B_{12}\) is used as an antipernicious anemia factor

Pernicious anemia is a condition caused by the inability to absorb Vitamin \(B_{12}\) from the diet. This can result from an autoimmune response that destroys stomach cells responsible for producing intrinsic factor, a protein necessary for Vitamin \(B_{12}\) absorption. Vitamin \(B_{12}\) is crucial for DNA synthesis and red blood cell formation. Without it, red blood cells cannot mature properly, leading to the production of abnormally large and dysfunctional red blood cells, a condition known as megaloblastic anemia. Vitamin \(B_{12}\) injections or high-dose oral supplements can be used to treat and prevent pernicious anemia.

3. Vitamin \(B_{12}\) is a cobalt complex in \(+III\) oxidation state

In cyanocobalamin, the cobalt ion is in the +3 oxidation state \((Co^{3+})\). This is the most stable and common oxidation state of cobalt in Vitamin \(B_{12}\). The coordination chemistry of Vitamin \(B_{12}\) involves the cobalt ion being bonded to the corrin ring (a modified porphyrin) and various axial ligands, including the cyanide group in cyanocobalamin. The other biologically active forms of Vitamin B12, methylcobalamin and adenosylcobalamin, also contain cobalt in the \(+3\) oxidation state, but with different groups attached.

Summary

All statements about Vitamin \(B_{12}\) being a cyanocobalamin complex, used as an antipernicious anemia factor, and containing cobalt in the +III oxidation state are accurate. Given these explanations, we can confidently conclude that:All are correct