In the Finkelstein reaction $\mathrm{R}-\mathrm{Cl}+\mathrm{NaI}\to \mathrm{R}-\mathrm{I}+\mathrm{NaCl}$, acetone is the preferred solvent because

1. Aacetone reacts with $\mathrm{NaCl}$ to remove it
2. B$\mathrm{NaI}$ dissolves in acetone but $\mathrm{NaCl}$ does not, so precipitation of $\mathrm{NaCl}$ drives the reaction forward
3. C$\mathrm{NaCl}$ dissolves much better than $\mathrm{NaI}$ in acetone
4. Dacetone is protic and strongly activates iodide