Which of the following is anodic reaction.

Options

A. `SO_(4)^(2-)+H_(2)O rarr H_(2)SO_(4)+1//2O_(2)+2e^(-)`
B. `H^(o+)+e^(-)rarr 1//2OH_(2)`
C. `Ag^(o+)+e^(-) rarr Ag`
D. None of these

Explanation

To determine which of the given reactions is an anodic reaction, we need to understand what an anodic reaction entails. An anodic reaction is characterized by oxidation, which involves the loss of electrons.

### Step-by-Step Solution:

1. **Identify the Reactions**: We have four reactions to analyze:
- A: \( \text{SO}_4^{2-} + \text{H}_2 \rightarrow \text{H}_2\text{SO}_4 + \frac{1}{2} \text{O}_2 + 2 \text{e}^- \)
- B: \( \text{H}^+ + \text{e}^- \rightarrow \frac{1}{2} \text{OH} \)
- C: \( \text{Ag}^+ + \text{e}^- \rightarrow \text{Ag} \)
- D: None of the above.

2. **Understand Oxidation**: Oxidation is defined as the loss of electrons, which means that if a species loses electrons, it is undergoing oxidation.

3. **Analyze Each Reaction**:
- **Reaction A**: \( \text{SO}_4^{2-} + \text{H}_2 \rightarrow \text{H}_2\text{SO}_4 + \frac{1}{2} \text{O}_2 + 2 \text{e}^- \)
- Here, \( \text{SO}_4^{2-} \) is losing electrons (2 electrons are produced), indicating oxidation.
- **Reaction B**: \( \text{H}^+ + \text{e}^- \rightarrow \frac{1}{2} \text{OH} \)
- In this reaction, \( \text{H}^+ \) is gaining an electron, indicating reduction.
- **Reaction C**: \( \text{Ag}^+ + \text{e}^- \rightarrow \text{Ag} \)
- Here, \( \text{Ag}^+ \) is also gaining an electron, indicating reduction.
- **Reaction D**: None of the above.

4. **Conclusion**: Since only Reaction A involves the loss of electrons, it is the only anodic reaction. Therefore, the correct answer is **Option A**.