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Narrative
These three test tubes contain a 2% solution of silver nitrate in ethanol. The isomeric halides 1-bromobutane, 2-bromobutane, and 2-bromo-2-methylpropane are added to separate test tubes. Reaction is indicated by the formation of a pale yellow precipitate of silver bromide.

Discussion
The tertiary halide 2-bromo-2-methylpropane immediately forms a light yellow precipitate of silver bromide. The secondary halide 2-bromobutane reacts next. The order of reactivity of tertiary > secondary > primary halides indicates a S_N1 mechanism.