The oxidation state of Cu in chalcopyrite is _________.

Answer

To determine the oxidation state of copper (Cu) in chalcopyrite, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the formula of chalcopyrite**:
The chemical formula of chalcopyrite is \( \text{CuFeS}_2 \).

2. **Assign oxidation states to known elements**:
- The oxidation state of iron (Fe) in chalcopyrite is typically +3 (ferric state).
- The oxidation state of sulfur (S) in sulfides is usually -2.

3. **Set up the equation for the oxidation states**:
Let the oxidation state of copper (Cu) be \( x \).
The overall charge of the compound must equal zero since it is neutral.
Therefore, we can write the equation based on the formula:
\[ x + (+3) + 2 \times (-2) = 0 \]

4. **Simplify the equation**:
\[ x + 3 - 4 = 0 \]
\[ x - 1 = 0 \]

5. **Solve for \( x \)**:
\[ x = +1 \]

6. **Conclusion**:
The oxidation state of copper (Cu) in chalcopyrite is +1.

### Final Answer:
The oxidation state of Cu in chalcopyrite is **+1**.