Answer is (a) Swart’s reaction
Alkyl fluorides which cannot be prepared by Finkelstein reaction is best accomplished by Swarts reaction.
In this reaction, the corresponding fluoride is obtained by the action of mercurous fluoride or antimony trifluoride on corresponding chlorides. The reaction is as follows:
2CH3CI + Hg2F2 → 2CH3F + Hg2CI2