Which of the following is a redox reaction?

Options

A. `2CuSO_(4) + 4KI to Cu_(2)I_(2) + 2K_(2)SO_(4) + I_(2)`
B. `SO_(3) + H_(2)O to H_(2)SO_(4)`
C. `Na_(2)SO_(4) + BaCl_(2) to BaSO_(4) + 2NaCl`
D. `CuSO_(4) + 4NH_(3) to [Cu(NH_(3))_(4)]SO_(4)`

Explanation

To determine which of the given reactions is a redox reaction, we need to analyze each reaction for changes in oxidation states. A redox reaction involves both oxidation (loss of electrons) and reduction (gain of electrons).

### Step-by-Step Solution:

1. **Identify the Reactions**:
We have the following reactions to analyze:
- Reaction 1: \( 2 \text{CuSO}_4 + 4 \text{KI} \rightarrow \text{Cu}_2\text{I}_2 + 2 \text{K}_2\text{SO}_4 + \text{I}_2 \)
- Reaction 2: \( \text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 \)
- Reaction 3: \( \text{Na}_2\text{SO}_4 + \text{BaCl}_2 \rightarrow \text{BaSO}_4 + 2 \text{NaCl} \)

2. **Analyze Reaction 1**:
- Determine oxidation states:
- In \( \text{CuSO}_4 \): Cu = +2, S = +6, O = -2
- In \( \text{KI} \): K = +1, I = -1
- In \( \text{Cu}_2\text{I}_2 \): Cu = +1, I = 0
- In \( \text{K}_2\text{SO}_4 \): K = +1, S = +6, O = -2
- In \( \text{I}_2 \): I = 0
- Changes:
- Cu changes from +2 to +1 (reduction, gain of electron)
- I changes from -1 to 0 (oxidation, loss of electron)
- Conclusion: This is a redox reaction.

3. **Analyze Reaction 2**:
- Determine oxidation states:
- In \( \text{SO}_3 \): S = +6, O = -2
- In \( \text{H}_2\text{O} \): H = +1, O = -2
- In \( \text{H}_2\text{SO}_4 \): H = +1, S = +6, O = -2
- Changes:
- No change in oxidation states for S, H, or O.
- Conclusion: This is not a redox reaction.

4. **Analyze Reaction 3**:
- Determine oxidation states:
- In \( \text{Na}_2\text{SO}_4 \): Na = +1, S = +6, O = -2
- In \( \text{BaCl}_2 \): Ba = +2, Cl = -1
- In \( \text{BaSO}_4 \): Ba = +2, S = +6, O = -2
- In \( \text{NaCl} \): Na = +1, Cl = -1
- Changes:
- No change in oxidation states for Na, S, O, Ba, or Cl.
- Conclusion: This is not a redox reaction.

5. **Final Conclusion**:
- The only reaction that involves both oxidation and reduction is Reaction 1. Therefore, it is the only redox reaction among the given options.

### Final Answer:
The redox reaction is:
**Reaction 1: \( 2 \text{CuSO}_4 + 4 \text{KI} \rightarrow \text{Cu}_2\text{I}_2 + 2 \text{K}_2\text{SO}_4 + \text{I}_2 \)**.

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