In which of the following reactions conc. `H_2SO_4` is not used as on oxidising agnet ?

Options

A. `Cu + 2H_2SO_4 to CuSO_4 + SO_2 + 2H_2O`
B. `2HI + H_2SO_4 to I_2 + SO_2 + 2H_2O`
C. `CaF_2 + H_2SO_4 rarr CuSO_4 + 2HF`
D. None

Answer

To determine which reaction does not use concentrated \( H_2SO_4 \) as an oxidizing agent, we need to analyze each option provided in the question.

### Step-by-Step Solution:

1. **Identify the Reactions**: We need to look at the reactions given in the options and identify the role of concentrated \( H_2SO_4 \) in each.

2. **Option A**:
- Reaction: \( Cu + 2H_2SO_4 \rightarrow CuSO_4 + SO_2 + 2H_2O \)
- Analysis: Copper (Cu) goes from an oxidation state of 0 to +2 in \( CuSO_4 \). This indicates that copper is oxidized. Since \( H_2SO_4 \) facilitates this oxidation, it acts as an oxidizing agent in this reaction.

3. **Option B**:
- Reaction: \( 2HI + H_2SO_4 \rightarrow I_2 + SO_2 + 2H_2O \)
- Analysis: Iodine (I) goes from -1 in \( HI \) to 0 in \( I_2 \). This indicates oxidation. The sulfur in \( H_2SO_4 \) goes from +6 to +4, meaning it is reduced. Thus, \( H_2SO_4 \) is acting as an oxidizing agent here as well.

4. **Option C**:
- Reaction: \( CaF_2 + H_2SO_4 \rightarrow CaSO_4 + 2HF \)
- Analysis: In this reaction, there is no change in the oxidation states of any of the elements involved. Calcium remains +2, sulfur remains +6, fluorine remains -1, and hydrogen remains +1. Since there is no oxidation or reduction occurring, \( H_2SO_4 \) does not act as an oxidizing agent in this reaction.

5. **Conclusion**: Based on the analysis, the reaction in **Option C** is the one where concentrated \( H_2SO_4 \) is not used as an oxidizing agent.

### Final Answer:
**Option C** is the reaction in which concentrated \( H_2SO_4 \) is not used as an oxidizing agent.

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