Final answer:
Cobalt is an essential component of Vitamin B12, necessary for nerve function and red blood cell production, and is involved in complex coordination compounds.
Step-by-step explanation:
The correct answer to the student's question is d) Vitamin B12. Cobalt is an essential component of Vitamin B12, also known as cobalamin, which is critical for proper nervous system function and the production of red blood cells. The structure of Vitamin B12 is quite complex and is classified as a coordination compound. This complex molecule contains cobalt in place of iron, which is found in similar compounds like hemoglobin. The cobalt in Vitamin B12 is actually bound to a corrin ring with long side chains, and it is linked to a molecule called 5,6-dimethylbenzimidazole. Furthermore, this cobalt complex is essential for animals and some protists, as well as for bacteria and cyanobacteria involved in nitrogen fixation.