Introduction:
Both naphthalene and benzene are aromatic hydrocarbons with a benzene ring structure. However, naphthalene is more reactive than benzene in electrophilic substitution reactions. This can be explained by the presence of two benzene rings in naphthalene and the greater electron density in these rings.

Structure:
Naphthalene consists of two benzene rings fused together, while benzene has a single benzene ring. The double ring structure in naphthalene makes it less stable compared to benzene.

Electron density:
Due to the presence of two benzene rings, naphthalene has a higher electron density compared to benzene. The pi electrons in the benzene rings of naphthalene are delocalized over a larger area, leading to a greater electron density in the ring system.

Reactivity:
The higher electron density in naphthalene makes it more reactive in electrophilic substitution reactions. In electrophilic substitution, an electrophile attacks the electron-rich aromatic ring, resulting in the substitution of a hydrogen atom. The greater electron density in naphthalene makes it more susceptible to attack by electrophiles.

Stabilization of intermediates:
In electrophilic substitution reactions, intermediate carbocation species are formed during the reaction. These carbocations are stabilized by resonance in the aromatic ring system. In naphthalene, due to the presence of two benzene rings, the positive charge in the intermediate can be delocalized over a larger area, providing greater stability to the intermediate species. This stabilization helps to lower the energy barrier for the reaction and increases the reactivity of naphthalene.

Aromaticity:
Although naphthalene is more reactive, benzene is considered more aromatic. Aromaticity is a property of compounds that have a continuous ring of atoms with a delocalized pi electron system. Benzene meets the criteria for aromaticity as it has a single, planar, and fully conjugated ring of carbon atoms with six pi electrons. Naphthalene, on the other hand, has two benzene rings, but they are not fully conjugated with each other, and the pi electron system is interrupted between them. Therefore, naphthalene is less aromatic compared to benzene.

Conclusion:
In summary, naphthalene is more reactive than benzene in electrophilic substitution reactions due to its higher electron density and the stabilization of intermediate carbocation species. However, benzene is considered more aromatic because it satisfies the criteria for aromaticity with its fully conjugated ring of carbon atoms.