Which of the following statement is/are true ?

Options

A. `Cu^(2+)` salts form soluble complex with excess KCN
B. `Cu^(2+)` salts form soluble complex with aqueous ammonia
C. `Cu^(2+)` salts form soluble complex with KI
D. A piece of iron or zinc when place in `Cu^(2+)` salt solution, precipitates copper

Explanation

To determine which statements are true regarding copper(II) ions (Cu²⁺) and their interactions with various ligands and metals, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement 1: Cu²⁺ salts form soluble complex with excess KCN.**
- When Cu²⁺ reacts with KCN, it initially forms cupric cyanide (Cu(CN)₂), which can precipitate. However, with excess KCN, it forms a soluble complex known as K₃[Cu(CN)₄].
- **Conclusion:** This statement is **true**.

2. **Statement 2: Cu²⁺ salts form soluble complex with aqueous ammonia.**
- Aqueous ammonia (NH₃) acts as a ligand and donates its lone pair of electrons to Cu²⁺ ions, forming a soluble complex known as [Cu(NH₃)₄]²⁺. This complex is indeed soluble in water.
- **Conclusion:** This statement is **true**.

3. **Statement 3: Cu²⁺ forms soluble complex with KI.**
- When Cu²⁺ reacts with KI, it forms a brown precipitate of Cu₂I₂. This indicates that no soluble complex is formed, as the reaction leads to precipitation rather than solubility.
- **Conclusion:** This statement is **false**.

4. **Statement 4: A piece of iron or zinc when placed in Cu²⁺ salt solution precipitates copper.**
- When a piece of zinc is placed in a Cu²⁺ salt solution (e.g., CuSO₄), zinc displaces copper due to its higher reactivity. The reaction can be represented as:
\[ \text{CuSO}_4 (aq) + \text{Zn} (s) \rightarrow \text{ZnSO}_4 (aq) + \text{Cu} (s) \]
- This results in the precipitation of copper metal.
- **Conclusion:** This statement is **true**.

### Final Summary:
- **True Statements:** 1, 2, and 4
- **False Statement:** 3