Which of the following is a chelate complex ion?

Options

A. `[Cu(en)_(2)]^(2+)`
B. `[CuCI_(4)]^(2-)`
C. `[Cu(NH_(3))_(4)]^(2-)`
D. `[Cu(CN)_(4)]^(3-)`

Answer

To determine which of the following is a chelate complex ion, we first need to understand what a chelate complex is. A chelate complex is formed when a ligand binds to a metal ion at two or more coordination sites, creating a ring-like structure.

### Step-by-Step Solution:

1. **Understand the Definition of a Chelate Complex:**
- A chelate complex is formed when a ligand, which has two or more donor atoms, binds to a metal ion at multiple sites. This results in the formation of a stable ring structure.

2. **Analyze the Given Options:**
- We need to examine each option provided to see which one has a ligand that can bind to the metal at two or more sites.

3. **Evaluate Each Option:**
- **Option 1:** If the ligand has two or more donor atoms that can bond with the metal ion, it can form a chelate complex.
- **Option 2:** If the ligand can only bond at one site, it cannot form a chelate complex.
- **Option 3:** Similar to Option 2, if the ligand has only one binding site, it will not form a chelate complex.
- **Option 4:** Check if the ligand has multiple donor atoms that can bond to the metal ion.

4. **Identify the Correct Chelate Complex:**
- After evaluating the options, identify which one has a ligand that can bind to the metal at two or more sites.
- For example, if you have a ligand like ethylenediamine (en), which has two nitrogen atoms that can coordinate to a metal ion, it would form a chelate complex.

5. **Conclusion:**
- Based on the analysis, select the option that represents a chelate complex ion. For instance, if Option 1 is C-U-E-N-2+, and it has a ligand that can bind at two sites, then it is the correct answer.

### Final Answer:
The correct answer is **Option 1**, which represents a chelate complex ion.