Which of the following ions form most stable complex compound

Options

A. `Cu^(++)`
B. `Ni^(++)`
C. `Fe^(++)`
D. `Mn^(++)`

Explanation

To determine which of the given ions forms the most stable complex compound, we will analyze the electronic configurations of the ions and their charge densities. Here’s a step-by-step solution:

### Step 1: Identify the electronic configurations of the ions
- **Copper (Cu²⁺)**: The atomic number of copper is 29. Its electronic configuration is:
- Neutral Cu: [Ar] 4s¹ 3d¹⁰
- Cu²⁺: After losing 2 electrons (1 from 4s and 1 from 3d), the configuration becomes [Ar] 3d⁹.

- **Nickel (Ni²⁺)**: The atomic number of nickel is 28. Its electronic configuration is:
- Neutral Ni: [Ar] 4s² 3d⁸
- Ni²⁺: After losing 2 electrons (both from 4s), the configuration becomes [Ar] 3d⁸.

- **Iron (Fe²⁺)**: The atomic number of iron is 26. Its electronic configuration is:
- Neutral Fe: [Ar] 4s² 3d⁶
- Fe²⁺: After losing 2 electrons (both from 4s), the configuration becomes [Ar] 3d⁶.

- **Manganese (Mn²⁺)**: The atomic number of manganese is 25. Its electronic configuration is:
- Neutral Mn: [Ar] 4s² 3d⁵
- Mn²⁺: After losing 2 electrons (both from 4s), the configuration becomes [Ar] 3d⁵.

### Step 2: Analyze charge density
Charge density is defined as the charge of the ion divided by its volume. Higher charge density generally leads to more stable complexes because it allows for stronger interactions with ligands.

### Step 3: Compare the charge densities
- **Cu²⁺** has a +2 charge and a relatively small ionic radius, leading to a high charge density.
- **Ni²⁺** has a +2 charge but a larger ionic radius than Cu²⁺, resulting in lower charge density.
- **Fe²⁺** also has a +2 charge with a larger ionic radius than Cu²⁺, leading to lower charge density.
- **Mn²⁺** has a +2 charge but with an even larger ionic radius, resulting in the lowest charge density among the four.

### Step 4: Conclusion
Since Cu²⁺ has the highest charge density, it forms the most stable complex compound among the given ions.

**Final Answer**: The ion that forms the most stable complex compound is **Cu²⁺**.

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