In the Finkelstein reaction, $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{Cl}$ is heated with $\mathrm{NaI}$ in dry acetone. The main product and the reason the reaction goes to completion are

1. A$\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{I}$; $\mathrm{NaI}$ is insoluble in acetone and precipitates
2. B$\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{F}$; $\mathrm{NaCl}$ is insoluble in acetone and precipitates
3. C$\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{OH}$; acetone supplies the hydroxyl group
4. D$\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{I}$; $\mathrm{NaCl}$ is insoluble in acetone and precipitates