Which of the following reactions is not used for the preparation of a colloidal solutions ?

Options

A. `2H_(2)S+SO_(2)rarr2H_(2)O+3S`
B. `2AuCI_(3)+3SnCI_(2)rarr3SnCI_(4)+2Au`
C. `FeCI_(3)+3H_(2)OrarrFe(OH)_(3)+3HCI`
D. `Fe_(3)O_(4)+4H_(2)rarr3Fe+4H_(2)O`

Answer

To determine which of the following reactions is not used for the preparation of colloidal solutions, we need to analyze each reaction provided in the options. A colloidal solution consists of a dispersed phase and a dispersion medium, with particle sizes typically ranging from 1 nanometer to 1000 nanometers.

### Step-by-Step Solution:

1. **Understanding Colloidal Solutions**:
- A colloidal solution is a heterogeneous mixture where tiny particles (dispersed phase) are distributed throughout a medium (dispersion medium). The particle size of colloids ranges from 1 nm to 1000 nm.

2. **Analyzing the First Reaction**:
- **Reaction**: H2S + SO2 → H2O + S
- **Analysis**: Sulfur (S) particles can aggregate to form colloidal particles within the size range of colloids. Therefore, this reaction can lead to the formation of a colloidal solution.

3. **Analyzing the Second Reaction**:
- **Reaction**: AuCl3 + SnCl2 → SnCl4 + Au
- **Analysis**: Gold (Au) particles are also very small and can combine to form a colloidal solution. This reaction is valid for the preparation of a colloidal solution.

4. **Analyzing the Third Reaction**:
- **Reaction**: FeCl3 + 3H2O → Fe(OH)3 + 3HCl
- **Analysis**: Ferric hydroxide (Fe(OH)3) can exist as a positively charged colloidal sol, which falls within the colloidal size range. Thus, this reaction can also produce a colloidal solution.

5. **Analyzing the Fourth Reaction**:
- **Reaction**: Fe3O4 + H2 → Fe + H2O
- **Analysis**: The products here do not lead to the formation of colloidal particles within the specified size range. The reaction primarily produces iron (Fe) and water, which does not yield a colloidal solution.

6. **Conclusion**:
- The reaction that does not lead to the formation of a colloidal solution is the fourth option: **Fe3O4 + H2 → Fe + H2O**.

### Final Answer:
The reaction that is not used for the preparation of a colloidal solution is **Option 4: Fe3O4 + H2 → Fe + H2O**.

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