In which of the following species is the charge delocalised by resonance?

A $CH X_{3} - COO X^{-}$
B $C X_{6} H X_{5} - O X^{-}$
C $CH X_{2} = CH - CH X_{2} X^{-}$
D $CH X_{3} - CH X_{2} - O X^{-}$

Answer: A, B, C

Allyl anion, acetate and phenoxide each have a lone pair or charge adjacent to a pi bond, so the charge is shared. Ethoxide has a localised charge on oxygen with no adjacent pi bond.

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