Which one of the following ion is aromatic ?

Options

A.
B.
C.
D.

Answer

To determine which ion is aromatic, we need to apply Huckel's rule of aromaticity. Here’s a step-by-step solution:

### Step 1: Understand Huckel's Rule
According to Huckel's rule, for a compound to be considered aromatic, it must satisfy the following criteria:
1. The compound must be cyclic (form a ring).
2. The compound must be planar.
3. The compound must have a continuous overlap of p-orbitals (conjugation).
4. The compound must contain \(4n + 2\) π electrons, where \(n\) is a non-negative integer (0, 1, 2, ...).

### Step 2: Analyze Each Option
Now, let's analyze the provided options one by one to check if they meet the criteria for aromaticity.

#### Option 1:
- **Structure**: Contains 2 π electrons.
- **Hybridization**: All atoms are sp² hybridized.
- **Planarity**: The structure is planar.
- **Conjugation**: Yes, there is conjugation.
- **π Electrons**: 2 π electrons (which fits \(4n + 2\) with \(n = 0\)).
- **Conclusion**: This ion is aromatic.

#### Option 2:
- **Structure**: Contains 4 π electrons.
- **Hybridization**: All atoms are sp² hybridized.
- **Planarity**: The structure is planar.
- **Conjugation**: Yes, there is conjugation.
- **π Electrons**: 4 π electrons (which does not fit \(4n + 2\)).
- **Conclusion**: This ion is not aromatic.

#### Option 3:
- **Structure**: Contains more than 2 π electrons.
- **Hybridization**: At least one atom is sp³ hybridized.
- **Planarity**: The structure is not planar due to sp³ hybridization.
- **Conclusion**: This ion is not aromatic.

#### Option 4:
- **Structure**: Similar to Option 3.
- **Hybridization**: At least one atom is sp³ hybridized.
- **Planarity**: The structure is not planar.
- **Conclusion**: This ion is not aromatic.

### Step 3: Final Conclusion
After analyzing all options, we find that only **Option 1** satisfies all the criteria for aromaticity. Therefore, the aromatic ion is:

**Answer: Option 1**

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