Final answer:
In ester synthesis, the organic layer which usually contains the ester should be kept, and it typically forms the top layer if the organic solvent is less dense than water.
Step-by-step explanation:
In ester synthesis, after the reaction is complete, typically two layers are formed due to the difference in polarity between the organic layer and the aqueous layer. The layer to be kept depends on where the ester product is more soluble and less dense. Generally, esters are organic compounds that are less dense than water and are often found in the organic layer. Since esters tend to have lower boiling points and cannot form hydrogen bonds as well as water, they are often found at the top if the organic solvent is less dense than water. Therefore, for the synthesis of an ester such as ethyl ethanoate (ethyl acetate), the correct answer would be a) Organic; top.