Explain with resons which of the following half reactions is oxidation and which is reduction?
`Hg_(2)^(2+)to2Hg^(2+)+2e^(-)`

Answer

To determine whether the half-reaction \( \text{Hg}_2^{2+} \rightarrow 2 \text{Hg}^{2+} + 2 e^{-} \) is an oxidation or reduction, we need to analyze the changes in oxidation states and the flow of electrons.

### Step-by-Step Solution:

1. **Identify the Half-Reaction**:
The half-reaction given is:
\[ \text{Hg}_2^{2+} \rightarrow 2 \text{Hg}^{2+} + 2 e^{-} \]

2. **Understand Oxidation and Reduction**:
- **Oxidation** is defined as the loss of electrons or an increase in oxidation state.
- **Reduction** is defined as the gain of electrons or a decrease in oxidation state.

3. **Analyze the Reactants and Products**:
- The reactant is \( \text{Hg}_2^{2+} \) (dimeric mercury ion).
- The products are \( 2 \text{Hg}^{2+} \) (two monomeric mercury ions) and \( 2 e^{-} \) (two electrons).

4. **Determine the Change in Oxidation States**:
- In \( \text{Hg}_2^{2+} \), the oxidation state of mercury is +1 (since it is a dimer, each mercury atom has an oxidation state of +1).
- In \( \text{Hg}^{2+} \), the oxidation state of mercury is +2.

5. **Identify Electron Flow**:
- The half-reaction shows that \( \text{Hg}_2^{2+} \) loses 2 electrons to form \( 2 \text{Hg}^{2+} \).
- Since electrons are being lost, this indicates oxidation.

6. **Conclusion**:
- Since there is a loss of electrons in the half-reaction, we conclude that this half-reaction is an **oxidation reaction**.

### Final Answer:
The half-reaction \( \text{Hg}_2^{2+} \rightarrow 2 \text{Hg}^{2+} + 2 e^{-} \) is an **oxidation reaction** because it involves the loss of electrons.

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