Describe the preparation of alkyl halides by halogen exchange reactions.

(N/A) Finkelstein Reaction: Alkyl iodides are often prepared by the reaction of alkyl chlorides or bromides with $NaI$ in dry acetone. This reaction is known as the Finkelstein reaction.
Reaction: $R-X + NaI \xrightarrow{\text{dry acetone}} R-I + NaX_{(s)}$
(where $X = Cl, Br$)
$NaCl$ or $NaBr$ formed precipitates in dry acetone,which facilitates the forward reaction according to Le Chatelier's principle.
$(b)$ Swarts Reaction: Alkyl fluorides are best prepared by heating an alkyl chloride or bromide in the presence of a metallic fluoride such as $AgF$,$Hg_2F_2$,$CoF_2$,or $SbF_3$. This reaction is known as the Swarts reaction.
Reaction: $H_3C-Br + AgF \rightarrow H_3C-F + AgBr$