To create reaction conditions suitable for an SN2 reaction, sodium iodide will be employed. Iodide is a great nucleophile, given its highly polarizable nature. Since SN2 reactions work best in an aprotic solvent, acetone will be utilized for these reactions. As a side product, the sodium cation will form an ionic compound with the leaving halides. Since sodium chloride and sodium bromide is not soluble in acetone, thus the successful substitution reaction of the halides will be confirmed visually by the formation of a salt precipitate. 

1. 1-bromobutane 

2. 2-bromobutane 

3. 1-chlorobutane