Which of the following structures are aromatic in nature?

For a compound to be aromatic, it must fulfill four criteria:

1. Cyclic: The structure must be a closed ring.
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2. Planar: All atoms in the ring must be $$sp^2$$ hybridized so the p-orbitals can align.
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3. Fully Conjugated: There must be a continuous system of alternating double bonds, positive charges, negative charges, or lone pairs around the entire ring.
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4. Hückel's Electron Count: The conjugated loop must contain $$(4n + 2)\,\pi$$ electrons (where $$n = 0, 1, 2, 3...$$, giving allowed counts of $$2, 6, 10, 14...\,\pi$$ electrons)
   

• A (Cyclopentadienyl Anion): Cyclic, planar, fully conjugated. It has 2 double bonds ($$4\pi$$ $$e^-$$) + 1 negative charge lone pair ($$2\pi$$ $$e^-$$) = $$6\pi$$ electrons ($$n=1$$). Aromatic.
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• B (Tropylium Cation): Cyclic, planar, fully conjugated. It has 3 double bonds ($$6\pi$$ $$e^-$$) + 1 empty p-orbital from the positive charge = $$6\pi$$ electrons ($$n=1$$). Aromatic.
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• C (Naphthalene): Cyclic, planar, fully conjugated bicyclic system. It has 5 double bonds = $$10\pi$$ electrons ($$n=2$$). Aromatic.
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• D (Cycloheptatrienyl Anion): It contains 3 double bonds ($$6\pi$$ $$e^-$$) + 1 negative charge lone pair ($$2\pi$$ $$e^-$$) = $$8\pi$$ electrons. This follows the $$4n$$ rule ($$n=2$$), making it Anti-aromatic (non-aromatic in reality as it tubs to lose planarity). Not Aromatic.