Which of the following combination of reagents does not undergo redox reaction in aqueous medium?

Options

A. `SnCl_(2)+HgCl_(2)`
B. `CuSO_(4)+KCN`
C. `Pb(CH_(3)COO)_(2)+KI`
D. `Ag_(2)O+SO_(2)`

Explanation

To determine which combination of reagents does not undergo a redox reaction in an aqueous medium, we need to analyze the oxidation states of the elements in each reaction. A redox reaction involves the transfer of electrons, resulting in changes in oxidation states: oxidation is an increase in oxidation state, while reduction is a decrease in oxidation state.

### Step-by-Step Solution:

1. **Identify the Reagents**: We have four combinations of reagents:
- A: Tin chloride and mercury(II) chloride
- B: Copper sulfate and potassium cyanide
- C: Lead acetate and potassium iodide
- D: Silver oxide and sulfur dioxide

2. **Analyze Combination A**:
- Tin chloride (SnCl2) and mercury(II) chloride (HgCl2) react to form mercury(I) chloride (Hg2Cl2) and tin(IV) chloride (SnCl4).
- Oxidation states:
- Sn changes from +2 to +4 (oxidation).
- Hg changes from +2 to +1 (reduction).
- This is a redox reaction.

3. **Analyze Combination B**:
- Copper sulfate (CuSO4) and potassium cyanide (KCN) react to form potassium sulfate (K2SO4), cyanogen (C2N2), and copper(I) cyanide (CuCN).
- Oxidation states:
- Cu changes from +2 to +1 (reduction).
- C changes from +2 to +1 (oxidation).
- This is a redox reaction.

4. **Analyze Combination C**:
- Lead acetate (Pb(CH3COO)2) and potassium iodide (KI) react to form lead(II) iodide (PbI2) and potassium acetate (CH3COOK).
- Oxidation states:
- Pb remains at +2.
- Iodine remains at -1.
- There are no changes in oxidation states; thus, this is not a redox reaction.

5. **Analyze Combination D**:
- Silver oxide (Ag2O) and sulfur dioxide (SO2) react to form silver sulfide (Ag2S) and oxygen (O2).
- Oxidation states:
- O changes from -2 to 0 (oxidation).
- S changes from +4 to -2 (reduction).
- This is a redox reaction.

6. **Conclusion**: Among the combinations analyzed, only combination C (lead acetate and potassium iodide) does not undergo a redox reaction. It is an ion exchange reaction.

### Final Answer:
The combination of reagents that does not undergo a redox reaction in aqueous medium is **C: Lead acetate and potassium iodide**.