By a proper choice of reagents, both symmetrical and unsymmetrical ethers can be prepared by Williamson synthesis which involves the reaction between an alkyl halide and an alkoxide ion. The reverse process involving the cleavage of ethers to give back the original alkyl halide and the alcohol can be carried out by heating the ether with HI at 373K.

Which of the following reagents when heated will give a good yield of ether? 

Sodium tert-butoxide and ethyl bromide 

$The$$correct\; answer\; is\; option\; 4.$Sodium tert-butoxide and ethyl bromide.

$tert$-Butyl ethyl ether can be prepared by the reaction of potassium $tert$-butoxide with ethyl bromide. The process is Williamson synthesis. This reaction follows S_N​2 mechanism.