Vitamin `B_(12)` deficiency causes pernicious anemia. Animals cannot synthesize vitamin `B_(12)`. Humans must obtain all their vitamin `B_(12)` from their diet. The complexing metal ion in vitamin `B_(12)` is :

Options

A. `Mg^(2+)` (Magnesium ion)
B. `Fe^(2+)` (Iron ion)
C. `Co^(3+)` (Cobalt ion)
D. `Zn^(2+)` (Zinc ion)