1. Identify what is being asked

We need the best method for synthesis of alkyl fluorides.

That is, we want a reaction that converts alkyl halides into alkyl fluorides efficiently.

2. Check each option

Option A: Sandmeyer’s reaction

Sandmeyer reaction is used mainly for converting aryl diazonium salts into aryl halides such as:

This is mainly useful for aryl chlorides, bromides, cyanides, etc., not for general preparation of alkyl fluorides.

So, A is incorrect.

Option B: Finkelstein reaction

Finkelstein reaction is halogen exchange typically used to prepare alkyl iodides from alkyl chlorides or bromides using sodium iodide in acetone:

It is especially useful for making iodides, not fluorides.

So, B is incorrect.

Option C: Swarts reaction

Swarts reaction is specifically used for preparing alkyl fluorides by heating alkyl chlorides or bromides with metallic fluorides such as $AgF$, $Hg_2F_2$, $CoF_2$, or $SbF_3$:

This is the standard and best-known method for synthesis of alkyl fluorides.

So, C is correct.

Option D: Free radical fluorination

Direct fluorination by free radical mechanism is highly uncontrolled because fluorine is extremely reactive. It often gives side reactions and is not the preferred method for preparing alkyl fluorides.

So, D is incorrect.

3. Conclusion

The best method for synthesis of alkyl fluorides is:

So the correct option is:

4. Comparison with stored correct answer

Stored correct answer: C

My derived answer: C

They match.