Which of the following reduction reactions are actually employed in commercial extraction of metals ?

Options

A. `Fe_(2)O_(3)+ 2Al to Al_(2)O_(3)+2Fe`
B. `Cr_(2)O_(3)+2Al to Al_(2)O_(3)+2Cr`
C. `2Na[Au(CN)_(2)]+Zn to Na_(2)[Zn(CN)_(4)]+2Au`
D. `Cu_(2)S+PB to Cu+PbS darr`

Answer

To determine which reduction reactions are employed in the commercial extraction of metals, we will analyze each of the given reactions step by step.

### Step 1: Identify the Reactions
We have the following reactions to consider:
1. **Fe2O3 + 2Al → Al2O3 + 2Fe** (Aluminothermic reaction)
2. **Cr2O3 + 2Al → Al2O3 + 2Cr** (Aluminothermic reaction)
3. **MacArthur-Forrest process for extracting Au and Ag**
4. **CuS + Pb → Cu + PbS** (Self-reduction)

### Step 2: Analyze Each Reaction
1. **Fe2O3 + 2Al → Al2O3 + 2Fe**
- This reaction involves the reduction of iron(III) oxide (Fe2O3) using aluminum. Although it produces iron, the process is highly costly due to the large amount of aluminum required. Therefore, it is not commonly used in commercial extraction.

2. **Cr2O3 + 2Al → Al2O3 + 2Cr**
- This reaction reduces chromium(III) oxide (Cr2O3) using aluminum. It is economically feasible and is employed in the industry for chromium extraction. Thus, this reaction is used commercially.

3. **MacArthur-Forrest Process**
- This process is used for the extraction of gold (Au) and silver (Ag). It involves the use of cyanide to leach the metals from their ores, making it a commercially viable method. Therefore, this process is also employed in the industry.

4. **CuS + Pb → Cu + PbS**
- This reaction is a self-reduction process where copper(I) sulfide (CuS) is reduced. However, it is not a feasible reaction for commercial extraction of copper due to the presence of lead and the inefficiency of the process in large-scale operations.

### Step 3: Conclusion
From the analysis:
- The reactions that are employed in commercial extraction of metals are:
- **Cr2O3 + 2Al → Al2O3 + 2Cr** (Aluminothermic reaction)
- **MacArthur-Forrest process for Au and Ag extraction**

### Final Answer
The reduction reactions employed in commercial extraction of metals are:
- Cr2O3 + 2Al → Al2O3 + 2Cr
- MacArthur-Forrest process for Au and Ag

---