The reactant atoms are copper, hydrogen, nitrogen, and oxygen. which reactant atom was oxidized in the reaction?

C. copper.

Explanation:

It is oxidation sate is changed from (+5) in the reactants (NO₃⁻) to (+4) in the products (NO₂). N gains 1 electron

So, it is reduced.

It is oxidation sate is the same (-2) in the reactants (NO₃⁻) and (-2) in the products (NO₂).

So, it is neither be oxidized nor reduced.

It is oxidation sate is changed (0) in the reactants (Cu) to (+2) in the products (Cu²⁺). Cu loses 2 electrons.

So, it is oxidized.

It is oxidation sate is the same (+1) in the reactants (H⁺) and (+1) in the products (H₂O).

So, it is neither be oxidized nor reduced.

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