Aromatic Substance Identification
To determine which of the given compounds is aromatic, we need to apply Huckel's rule and analyze each compound based on its structure and stability.
Criteria for Aromaticity
- Cyclic Structure: The compound must be cyclic.
- Planarity: The structure must be flat to allow for the overlap of p-orbitals.
- Conjugation: There must be a continuous system of p-orbitals (alternating single and double bonds).
- Huckel's Rule: The compound must have (4n + 2) π electrons, where n is a non-negative integer.
Analysis of Each Compound
- Cyclohexane (a):
- Not aromatic as it is a saturated compound with no double bonds.
- It has no π electrons.
- Naphthalene (b):
- Aromatic because it is a cyclic compound with a conjugated system.
- Contains 10 π electrons (5 double bonds), satisfying Huckel's rule (n=2).
- Cyclooctatraene (c):
- Although it has a cyclic structure and alternating double bonds, it is not planar.
- It has 8 π electrons, which does not satisfy Huckel's rule.
- 1,3-Butadiene (d):
- Linear and does not have a cyclic structure.
- Lacks the necessary characteristics for aromaticity.
Conclusion
The only aromatic substance among the options provided is:
- Naphthalene (b): It fits all criteria for aromaticity and is a stable compound due to its delocalized electrons.

Option B is correct. Napthalien is an aromatic compound.
Conditions for aromaticity are :
1 resonance in the compound (ring structure)
2 planar structure of compound
3 compound should have 4n+2 pi electrons

Cyclooctatetraene is an unsaturated cyclooctane, with non planar structure, hence it is not an aromatic compound.

Remaining 2 compounds are non aromatic becoz of lack of resonance (cyclohexane) or lack of ring structure (1,3 butdiene).