Which metal cannot be used as a reducing agent in smelting ?

Options

A. C
B. Al
C. Cu
D. Na

Explanation

To determine which metal cannot be used as a reducing agent in smelting, we need to understand the smelting process and the role of reducing agents.

### Step-by-Step Solution:

1. **Understanding Smelting**:
- Smelting is a process used to extract metals from their ores by heating them to high temperatures. This process often involves the reduction of metal oxides to obtain the pure metal.

2. **Role of Reducing Agents**:
- Reducing agents are substances that donate electrons to another substance, reducing its oxidation state. In smelting, they help in reducing metal ores to their elemental form.

3. **Common Reducing Agents**:
- The most commonly used reducing agents in smelting include carbon (in the form of coke), aluminum, and sodium. These substances are effective in reducing metal ores due to their high reactivity.

4. **Identifying the Metal in Question**:
- Among the metals considered, copper is mentioned. Copper is less electropositive and less reactive compared to other metals like aluminum and sodium.

5. **Conclusion**:
- Since copper does not have strong reducing properties and is not reactive enough to act as a reducing agent in smelting, it cannot be used for this purpose.

### Final Answer:
Copper cannot be used as a reducing agent in smelting.