Which of the following statements 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) salts and their reactions, we will evaluate each statement one by one.

### Step 1: Analyze Statement 1
**Statement:** Copper(II) salts form soluble complexes with excess KCN.

**Analysis:**
When copper(II) ions (Cu²⁺) react with excess potassium cyanide (KCN), they form a soluble complex known as cupric cyanide, represented as K₃[Cu(CN)₄]. This complex is indeed soluble in water.

**Conclusion:** Statement 1 is **True**.

### Step 2: Analyze Statement 2
**Statement:** Copper(II) salts form soluble complexes with aqueous ammonia.

**Analysis:**
Copper(II) ions react with ammonia (NH₃) to form a soluble complex, specifically [Cu(NH₃)₄]²⁺. This complex is stable and soluble in aqueous solution.

**Conclusion:** Statement 2 is **True**.

### Step 3: Analyze Statement 3
**Statement:** Copper(II) salts form soluble complexes with KI.

**Analysis:**
When copper(II) ions react with potassium iodide (KI), they do not form a soluble complex. Instead, they form a brown precipitate of copper(I) iodide (CuI) and iodine (I₂). Therefore, no soluble complex is formed in this reaction.

**Conclusion:** Statement 3 is **False**.

### Step 4: Analyze Statement 4
**Statement:** A piece of iron or zinc when placed in copper(II) salt solutions precipitates copper.

**Analysis:**
When a piece of zinc or iron is placed in a solution of copper(II) sulfate (CuSO₄), a displacement reaction occurs. Zinc or iron displaces copper, leading to the formation of zinc sulfate (ZnSO₄) or iron sulfate (FeSO₄) and precipitating copper metal.

**Conclusion:** Statement 4 is **True**.

### Final Conclusion:
The true statements are:
- **Statement 1:** True
- **Statement 2:** True
- **Statement 3:** False
- **Statement 4:** True

Thus, the correct options are **A, B, and D**.

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