The third reaction of the zinc-releasing electron and zinc ion will occur as the half-reaction at the anode of the voltaic cell. Thus, option 3 is the correct option.
What is a half-reaction?
A half-reaction is a depiction of the oxidation or the reduction half of a redox reaction that involves the stating of the oxidation states and the release or the absorption of the electrons.
The anode is an electrode of the voltaic cell where the oxidation reaction takes place. The oxidation results in the loss of the electrons and hence, reactions 1 and 2 cannot occur at the anode. The fourth reaction is also not possible as iron cannot lose its electron.
Therefore, option 3. Zn → Zn²⁺ + 2e⁻ will occur at the anode.
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