Which is not stable at room temperature ?

Options

A.
B.
C.
D.

Explanation

To determine which compound is not stable at room temperature, we need to analyze the stability of the compounds based on their aromaticity. Here’s a step-by-step solution:

### Step 1: Identify the Types of Compounds
We have four types of compounds to consider:
1. Non-aromatic
2. Non-aromatic
3. Anti-aromatic
4. Aromatic (Benzene)

### Step 2: Understand Aromaticity
Aromatic compounds are generally more stable due to their cyclic structure and delocalized pi electrons. Non-aromatic compounds do not have this stability, and anti-aromatic compounds are less stable than non-aromatic compounds due to their cyclic structure and the presence of 4n π electrons, which leads to destabilization.

### Step 3: Compare Stability
- **Aromatic Compounds**: Most stable due to resonance and delocalization of electrons.
- **Non-aromatic Compounds**: Stable but less so than aromatic compounds.
- **Anti-aromatic Compounds**: Least stable due to the destabilizing effects of having 4n π electrons.

### Step 4: Identify the Least Stable Compound
Since anti-aromatic compounds are the least stable, we can conclude that the third compound, which is anti-aromatic, is not stable at room temperature.

### Conclusion
The compound that is not stable at room temperature is the third option, which is anti-aromatic.

### Final Answer
**Option 3 is the correct answer, as it is anti-aromatic and thus the least stable.**

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