Pick out wrong combination:
(A) $F{{e}^{+2}}\to $ Haemoglobin
(B) $M{{g}^{2+}}\to $ Photosynthesis
(C) $S{{e}^{2+}}\to $ Krebs cycle
(D) \[C{{o}^{2+}}\to \] Vitamin B-12

Hint: Recall various processes given in the above options and try to correlate them with the metal ion given beside them for example in photosynthesis chlorophyll plays the key role, so check the relationship of chlorophyll with $M{{g}^{2+}}$, similarly check the relationship among each of the options given above.

Complete Step by Step Solution:
Haemoglobin contains iron in the form of $F{{e}^{+2}}$ (even myoglobin contains iron in the same form), it is this iron that binds to oxygen molecules, oxygen acts as ligand forming a co-ordinate bond with the $F{{e}^{+2}}$ion. The co-ordinate bond is slightly weak so that the oxygen can be released easily wherever it is required, so the data in option (A) is correct and hence option (A) is not the correct answer.

Chlorophyll pigment is very essential for photosynthesis to take place. $M{{g}^{2+}}$ is the central core of chlorophyll molecule in plant tissue, so if $M{{g}^{2+}}$is deficient this leads to shortage of chlorophyll which results in poor and stunted plant growth. Also, $M{{g}^{2+}}$ regulate the activities of key photosynthetic enzymes. $M{{g}^{2+}}$ ion helps chlorophyll to absorb light. Therefore option (B) is also not the correct answer.
\[C{{o}^{2+}}\] is very important for the formation of vitamin B-12. Vitamin B-12 is also known as cobalamin. It is cobalt containing ring-contracted modified tetrapyrolle that represents one of the most complex molecules made in nature. So option (D) is also incorrect.

\[S{{e}^{2+}}\] Does not play any role in Krebs cycle therefore option (C) is the correct answer.

Note: Different types of metal ions are used in various different processes, they may even form the structure of haemoglobin, chlorophyll etc. or may even be involved at enzymatic level of the process. A single metal ion can be involved in different processes and also a single process may involve various metal ions as well.