Alkyl fluorides can be synthesized by heating an alkyl chloride/bromide in the presence of a metallic fluoride such as AgF, Hg₂F₂, CoF₂ or SbF₃. The reaction is termed as Swarts reaction. Out of the given options, CoF₂ and Hg₂F₂, work as reagents. NaF cannot be used because the end products of NaF + RCl → RF + NaCl are soluble in the solvent i.e. water, making it difficult to separate. Hence the correct options are (ii) and (iii).