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JEE Main levelSingle correct optionDifficulty 2 of 3hc153

Which of the following species is aromatic?

Acyclopropenyl anion, $C X_{3} H X_{3} X^{-}$
Bcyclopentadienyl anion, $C X_{5} H X_{5} X^{-}$
Ccycloocta-1,3,5,7-tetraene, $C X_{8} H X_{8}$
Dcyclopentadienyl cation, $C X_{5} H X_{5} X^{+}$

Answer: B

Aromatic = planar, cyclic, fully conjugated,

(4 n + 2) π

electrons.

C X_{5} H X_{5} X^{-}

has 6 pi electrons. The cation (4 pi) and the cyclopropenyl anion (4 pi) are antiaromatic, and cyclooctatetraene (8 pi, non-planar tub) is non-aromatic.

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