The rate law of an E2 reaction of bromoethane with ethoxide ion in ethanol is

A $rate = k [RBr]$
B $rate = k [RBr] [C X_{2} H X_{5} O X^{-}]$
C $rate = k [C X_{2} H X_{5} O X^{-}]$
D $rate = k [RBr]^{2}$

Answer: B

E2 is a one-step bimolecular process in which the base removes a beta-hydrogen while the leaving group departs; both the substrate and the base are involved in the transition state, so rate =

k [RBr] [C X_{2} H X_{5} O X^{-}]

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