Cobalt is present in the molecule of
(a) vitamin B6
(b) vitamin B12
(c) vitamin B2
(d) vitamin B1
(b) Vitamin B12 (also called cobalamine) has a complex ring structure, similar to a porphyrin ring, to which is added a cobalt ion at its centre. This vitamin is synthesised exclusively by microorganisms. Thus, it is absent from plants, unless they re contaminated by microorganisms, but is conserved in animals in the river, where it is found as methylcobalamine, adenosylcobalamin, and hydroxocobalamin.