Imagine that you have isolated a mysterious liquid from a sample of food. you add the liquid to a beaker of water and shake vigorously. after a few minutes, the water and the other liquid separate into two layers. to which class of biological molecules does the unknown liquid most likely belong

I believe the liquid is in a class of biological molecules called  lipids. One property of lipid is that they are water soluble (hydrophobic), a property that is put to use in the organisation of cells and tissues. Therefore, lipids can not form bonds with water because they are non-polar and therefore a mixture of lipids and water is immiscible, like the case of the liquid of concern.