Solution

A. The reaction given in option A is correct. The preparation of higher alkanes from lower alkyl halides using sodium metal is called as Wurtz reaction. When two molecules of ethyl iodide are treated with sodium metal in the presence of diethyl ether as solvent, n-butane is formed.
B. The reaction given in option B is incorrect. When sodium metal in Wurtz reaction is replaced by zinc metal, then that reaction is called as Frankland reaction and it also gives a higher alkane as the product. Hence the product of the reaction given in option B should be n-butane.
C. Williamson synthesis of alkyl sulfides is carried out by treating alkyl halides with sodium sulfide. The reaction given in option C is correct.
D. When alkyl bromide is treated with NaI and acetone, then halogen exchange reaction takes place to give alkyl iodide as the product. This is called as Finkelstein reaction. Hence the reaction given in option D is also correct.