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 aqueous medium, we will analyze each of the provided options step by step.

### Step 1: Analyze the first reaction (SnCl2 + HgCl2)
- **Reactants**: SnCl2 (tin(II) chloride) and HgCl2 (mercury(II) chloride).
- **Products**: The reaction produces Hg (mercury metal) and SnCl4 (tin(IV) chloride).
- **Oxidation States**:
- Sn in SnCl2: +2
- Hg in HgCl2: +2
- Hg in the product: 0
- Sn in SnCl4: +4
- **Conclusion**: The oxidation state of Sn increases (from +2 to +4) and Hg decreases (from +2 to 0). This is a redox reaction.

### Step 2: Analyze the second reaction (CuSO4 + KCN)
- **Reactants**: CuSO4 (copper(II) sulfate) and KCN (potassium cyanide).
- **Products**: The reaction forms K2SO4 and CuCN (copper(I) cyanide).
- **Oxidation States**:
- Cu in CuSO4: +2
- Cu in CuCN: +1
- CN in KCN: -1
- CN in gaseous CN2: 0
- **Conclusion**: The oxidation state of Cu decreases (from +2 to +1) and CN increases (from -1 to 0). This is a redox reaction.

### Step 3: Analyze the third reaction (Pb(CH3COO)2 + KI)
- **Reactants**: Lead(II) acetate (Pb(CH3COO)2) and potassium iodide (KI).
- **Products**: The reaction produces PbI2 (lead(II) iodide) and CH3COOK (potassium acetate).
- **Oxidation States**:
- Pb in Pb(CH3COO)2: +2
- Pb in PbI2: +2
- I in KI: -1
- I in PbI2: -1
- **Conclusion**: There is no change in oxidation states for any of the elements involved. This is not a redox reaction.

### Step 4: Analyze the fourth reaction (Ag2O + SO2)
- **Reactants**: Silver(I) oxide (Ag2O) and sulfur dioxide (SO2).
- **Products**: The reaction produces Ag (silver metal) and SO3 (sulfur trioxide).
- **Oxidation States**:
- Ag in Ag2O: +1
- Ag in the product: 0
- S in SO2: +4
- S in SO3: +6
- **Conclusion**: The oxidation state of Ag decreases (from +1 to 0) and S increases (from +4 to +6). This is a redox reaction.

### Final Conclusion
After analyzing all reactions, the only reaction that does not undergo a redox reaction is the third reaction: **Pb(CH3COO)2 + KI**.

### Answer
The combination of reagents that does not undergo a redox reaction in aqueous medium is:
**Option 3: Pb(CH3COO)2 + KI**