Cu → cu2 2e– this equation represents

Explanation:

In a reduction-half reaction, there is gain of electrons.

For example,

Whereas in an oxidation-half reaction, there is loss of electrons.

For example,

Thus, we can conclude that the equation Cu → cu2 2e–  represents oxidation-half reaction.

the answer to your question is c.

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it means there are 3 atoms of oxygen