Answer:
B.Conversion of cation to atom
Step-by-step explanation:
Reduction involves the gaining of electrons. Since a cation is positively charged and has lost electrons, for it to become an atom and be neutral it would have to gain electrons that were previously lost before, hence the answer is B.
It cannot be A because an anion is negatively charged and has gained electrons. For the conversion of the anion to become an atom it would have to lose electrons to become neutral as before it has gained electrons, so oxidation (which is the loss of electrons) would occur.