Which one is not called a anode reaction from the following?

Options

A. `Cl^(-) to (1)/(2) Cl_(2) + e^(-)`
B. `Cu to Cu^(+ +) + 2e^(-)`
C. `Hg^(+) to Hg^(+ +) + e^(-)`
D. `Zn^(2+) + 2 e^(-) to Zn`

Explanation

To determine which reaction is not an anode reaction, we need to understand the concept of anode reactions in electrochemistry. Anode reactions are characterized by oxidation, where a species loses electrons, resulting in an increase in its oxidation state.

### Step-by-Step Solution:

1. **Understand the Definition of Anode Reaction:**
- An anode reaction involves oxidation, which means that a substance loses electrons and its oxidation state increases.

2. **Identify the Oxidation States:**
- For each reaction provided in the options, identify the oxidation states of the reactants and products.

3. **Analyze Each Reaction:**
- **Reaction 1:** If a metal ion A²⁺ is oxidized to A³⁺, it loses one electron. This is an oxidation process (anodic reaction).
- **Reaction 2:** If copper (Cu) goes from 0 to +2 oxidation state, it loses two electrons. This is also an oxidation process (anodic reaction).
- **Reaction 3:** If mercury (Hg) goes from +1 to +2 oxidation state, it loses one electron. This is again an oxidation process (anodic reaction).
- **Reaction 4:** If zinc (Zn) goes from +2 to 0 oxidation state, it gains electrons (reduction). This is not an oxidation process and therefore not an anodic reaction.

4. **Conclusion:**
- Based on the analysis, the reaction where zinc (Zn) goes from +2 to 0 is not an anode reaction because it involves reduction, not oxidation.

### Final Answer:
The reaction that is not called an anode reaction is the one where zinc (Zn) is reduced from +2 to 0.

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