Answer:
C
Step-by-step explanation:
The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element. However, in an ionic compound, one element’s atoms (especially metals) donate their valence electron(s) to the other element's atoms forming ionic bonds. This way, they achieve stable electron configuration. The oxidation number of an atom in this ionic bond will depend on how many valence electrons are lost (to produce positive oxidation number) or gained (to produce negative oxidation number).