Which of the following is anti-aromatic in nature?

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds is anti-aromatic in nature, we need to evaluate each compound based on the criteria for anti-aromaticity. A compound is considered anti-aromatic if it meets the following conditions:

1. It must be cyclic.
2. It must have conjugation (alternating double and single bonds).
3. It must be planar.
4. It must have 4n π electrons, where n is a non-negative integer (0, 1, 2, ...).

Now, let's analyze each compound step by step.

### Step 1: Analyze Cyclo-octa-tetraene
- **Cyclic**: Yes, it is a cyclic compound.
- **Conjugation**: Yes, it has alternating double bonds.
- **Planar**: No, cyclo-octa-tetraene is non-planar.
- **Electrons**: It has 8 π electrons (which is 4n for n=2).

**Conclusion**: Since it is not planar, cyclo-octa-tetraene cannot be anti-aromatic.

### Step 2: Analyze the Second Compound (Assuming it has 4 π electrons)
- **Cyclic**: Yes, it is a cyclic compound.
- **Conjugation**: Yes, it has conjugated double bonds.
- **Planar**: Yes, it is planar.
- **Electrons**: It has 4 π electrons (which is 4n for n=1).

**Conclusion**: This compound satisfies all conditions for anti-aromaticity. Therefore, it is anti-aromatic.

### Step 3: Analyze the Third Compound (Assuming it has a five-membered ring)
- **Cyclic**: Yes, it is cyclic.
- **Conjugation**: No, it does not have conjugated double bonds.
- **Planar**: No, it is non-planar due to the presence of an sp3 hybridized carbon.
- **Electrons**: Not applicable since it is non-conjugated.

**Conclusion**: This compound is non-aromatic due to lack of conjugation and non-planarity.

### Step 4: Analyze Aniline
- **Cyclic**: Yes, it is cyclic.
- **Conjugation**: Yes, it has conjugated double bonds.
- **Planar**: No, it is non-planar due to the nitrogen atom's lone pair.
- **Electrons**: It has 10 π electrons (which is 4n + 2 for n=2).

**Conclusion**: Aniline is non-aromatic because it is non-planar and has 10 π electrons, which does not fit the criteria for anti-aromaticity.

### Final Conclusion
After analyzing all the compounds:
- The only compound that is anti-aromatic is the second compound with 4 π electrons.

### Answer
**The anti-aromatic compound is option B.**