Cobalt is present in which vitamin?

Ans. is 'd' i.e., Vitamin B12* Vitamin B1 or thiamine is structurally an aminopyrimidine ring linked by a methylene bridge with a thiazole ring* Hence thiamine is a sulphur containing vitamin* Vitamin B3 or niacin is structurally nicotinic acid and it is C6H5N02. It has nitrogen and not cobalt* Vitamin B5 or pantothenic acid is pantoic acid linked to p alanine. It's coenzyme form is CoA. Coenzyme A is p mercaptoethanolamine linked to pantothenic acid and 3'5'ADP. Hence it does not have cobalt.* Vitamin B12 has cobalt present in the centre of a planar tetrapyrrole ring. So four of the valencies of cobalt are satisfied by the four pyrrole rings. Fifth valency is satisfied by dimethylbenzimidazole group.