Final answer:
The liquid in Layer 3 of the beaker will be the one with the lowest density, which is vegetable oil. It will float above the other liquids, such as water and syrup, and have a convex meniscus.
Step-by-step explanation:
The liquid that will be in Layer 3 of the teacher's experiment depends on the density of the liquids involved. Based on density and the given options, vegetable oil would likely be in Layer 3, as it tends to have a lower density compared to water and some types of syrup, meaning it would float above these other liquids when they are combined.
Referring to the provided reference notes, Table 1.7.1 indicates that corn oil (similar to vegetable oil) has a lower mass to volume ratio than water, thereby suggesting that it will float, which confirms our initial deduction. Rubbing alcohol, or isopropyl alcohol, is denser than oils and therefore would not be in the top layer. Hence, the correct answer is D) Vegetable Oil.