Final answer:
Methanol is miscible with water and would not form a separate layer for an efficient aqueous acid-base extraction, making it an unsuitable solvent for this process compared to other immiscible options.
Step-by-step explanation:
In an aqueous acid-base extraction, the solvent used needs to be immiscible with water so that it forms a separate layer, which allows for the selective partitioning of compounds based on their acidity or basicity. Out of the provided options, methanol (d) could not be used for this purpose because it is miscible with water.
Thus, it would not form a separate layer and would not allow for efficient separation during the extraction process. The solvents that are immiscible with water and could be used in aqueous acid-base extraction are ethyl acetate, diethyl ether, methylene chloride, hexane, and chloroform.