Benzene (c1ccccc1) is the parent aromatic hydrocarbon; its six C-C bonds are all 1.39 Å due to complete delocalization of 6 pi electrons across the planar ring. Huckel's Rule states that a compound is aromatic if it is planar, cyclic, fully conjugated, and has (4n+2) pi electrons (benzene: n=1, 6 pi $e^{-}$). Anti-aromatic compounds (4n pi $e^{-}$, planar, cyclic, conjugated) are destabilized; cyclobutadiene (4 pi $e^{-}$) is the classic example. Cyclooctatetraene (COT, 8 pi $e^{-}$) is non-aromatic, not anti-aromatic, because it adopts a non-planar tub conformation. Electrophilic Aromatic Substitution (EAS) proceeds via electrophile generation, electrophilic attack on the pi cloud forming the arenium ion (the rate-determining step), then proton loss to restore aromaticity. The five major EAS reactions are halogenation, nitration, sulfonation (the only reversible one), Friedel-Crafts alkylation, and Friedel-Crafts acylation. Ortho-para directors (-OH, -$NH_{2}$, -$CH_{3}$, -OR) donate electrons to the ring and increase reactivity; halogens are the unique o/p directors that are also deactivating (dominant -I effect). Meta directors (-$NO_{2}$, -CN, -CHO, -COOH, -COR) withdraw electrons by -M and deplete ortho/para more than meta, so electrophiles attack meta. Friedel-Crafts acylation is preferred over alkylation because the acylium ion (R$CO^{+}$) is resonance-stabilized (no rearrangement) and the -COR product deactivates the ring (no polyacylation). NEET consistently tests the halogen anomaly, the FC acylation advantage, and aromaticity classification by Huckel's Rule.