Here is the overall reaction of a mercury oxide dry cell: Zn + HgO ---> ZnO + Hg. In this reaction, which of the following gets oxidized?

Here is the overall reaction of a mercury oxide dry cell: Zn + HgO ---> ZnO + Hg. In this reaction, which of the following gets oxidized?

Hg
Zn
O
HgO


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Zinc is oxidized because it starts as a metal with an oxidation state of zero and ends up as an atom bound to oxygen. Oxygen has two bonds, so the oxidation state of Zinc would be 2. The Mercury is therefore reduced, because it undergoes the opposite process. This is a REDOX reaction, and the two half reactions are:

Zn -> Zn(+2) + 2e(-)
Hg(+2) + 2e(-) -> Hg