Which of the following nucleophiles is going to promote an SN2 reaction?
The SN2 reactions tend to proceed with strong nucleophiles; by this, generally means negatively charged nucleophiles such as I−,CH3O−,CN−,RS−,N3−,HO−, and others.
The SN1 tends to proceed with weak nucleophiles – generally neutral compounds such as solvents like CH3OH,H2O,CH3CH2OH
In the given options only NaI has I− a negative nucleophile.So NaI promotes SN2 reaction mechanism.
Hence option A is correct.