When KCN is added to `CuSO_(4)` solution:

Options

A. KCN acts an reducing agent
B. KCN acts as an complexing agent
C. `K_(3)[Cu(CN)_(4)]` is formed
D. All are correct

Answer

To solve the question regarding the reaction between KCN and CuSO4, we will analyze the steps involved in the reaction and the roles played by KCN.

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactants in this reaction are Potassium Cyanide (KCN) and Copper(II) Sulfate (CuSO4).

2. **Initial Reaction**:
- When KCN is added to CuSO4, the first step involves the formation of Copper(I) Cyanide (CuCN) and Potassium Sulfate (K2SO4).
- The reaction can be represented as:
\[ \text{CuSO}_4 + 2 \text{KCN} \rightarrow \text{CuCN}_2 + \text{K}_2\text{SO}_4 \]

3. **Disproportionation of CuCN**:
- The formed CuCN can undergo disproportionation, where it breaks down into Copper(I) Cyanide (CuCN) and Copper(II) Cyanide (Cu2CN2) along with the release of cyanide ions.
- This can be represented as:
\[ 2 \text{CuCN} \rightarrow \text{Cu}_2\text{CN}_2 + \text{CN}_2 \]

4. **Formation of the Complex**:
- The Copper(I) Cyanide (Cu2CN2) can further react with KCN to form a complex known as Potassium Tetracyanocuprate(II), represented as K3Cu(CN)4.
- The reaction can be summarized as:
\[ \text{Cu}_2\text{CN}_2 + 4 \text{KCN} \rightarrow \text{K}_3\text{Cu(CN)}_4 \]

5. **Roles of KCN**:
- KCN acts as a **reducing agent** because it reduces Copper(II) ions (Cu²⁺) to Copper(I) ions (Cu⁺), indicating a decrease in oxidation state.
- KCN also acts as a **complexing agent** since it forms a stable complex with Copper(I) ions.

6. **Final Conclusion**:
- All the statements regarding the reaction are correct:
- KCN acts as a reducing agent.
- KCN acts as a complexing agent.
- The complex K3Cu(CN)4 is formed.
- Therefore, the correct choice is that all statements are correct.

### Final Answer:
The correct option is that all statements are correct.

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