Rank the Starting Materials in Terms of Their Rate of Product

Essay

Rank the starting materials in terms of their rate of product formation in a reaction with sodium fluoride in dimethylformamide (1 being the fastest and 5 being the slowest). (Dimethylformamide (DMF) is a polar aprotic solvent.)
$\mathrm { Na } ^ { + } \mathrm { F } ^ { - } + \mathrm { R } - \mathrm { X } \stackrel { \mathrm { DMF } } { \longrightarrow } \mathrm { R } - \mathrm { F } + \mathrm { Na } ^ { + } \mathrm { X } ^ { - }$ ​