what is the best combination for preparing CH3CH2CH2CH2OCH3 is

CH3CH2CH2CH2OH+NaOCH3
CH3CH2CH2CH2ONa+NaOCH3
CH3CH2CH2CH2Br+NaOCH3
CH3CH2CH2CH2Br+CH3Br

Butyl chloride and sodium methoxide (find them) is your best bet.

In my previous answer I meant that butyl bromide not butyl chloride, reacting with sodium methoxide would produce the ether 1-methoxybutane, or methylbuthyl ether. The reagent, butyl bromide is also called 1-bromobutane in the IUPAC system of naming organic compounds.

To prepare CH3CH2CH2CH2OCH3 (ethyl methyl ether), you need to look for a combination that involves the reaction of an alcohol and a methylating reagent.

Among the given options, the best combination for preparing CH3CH2CH2CH2OCH3 is CH3CH2CH2CH2OH+NaOCH3. This combination involves the reaction between the alcohol CH3CH2CH2CH2OH (1-butanol) and the methylating reagent NaOCH3 (sodium methoxide). The sodium methoxide acts as a strong base and displaces the hydroxyl group (-OH) of 1-butanol, resulting in the formation of CH3CH2CH2CH2OCH3.

To determine the best combination, it is important to consider the reactivity of the reactants and the desired product. In this case, 1-butanol is the appropriate alcohol to react with sodium methoxide to form ethyl methyl ether. The other options do not involve the suitable reagents for the desired reaction.