Final answer:
Diethyl ether, CH3CH2OCH2CH3, is classified as a Lewis base because it has an oxygen atom with lone pairs of electrons that can be donated to form a coordinated covalent bond.
Step-by-step explanation:
When examining the molecule CH3CH2OCH2CH3, we look at its ability to donate or accept protons or electron pairs to determine its classification as an acid or base. According to Brønsted-Lowry theory, a base is a species that can accept a proton, while an acid is a species that can donate a proton. This molecule, also known as diethyl ether, cannot donate a proton, so it is not a Brønsted-Lowry acid. However, the oxygen atom in the ether has two lone pairs of electrons that can be donated to form a coordinate covalent bond; this makes it a Lewis base. Therefore, the correct classification for this molecule would be a Lewis base, option d.