Final answer:
When oil is mixed with water, they form separate layers because oil is nonpolar and water is polar, and oil is less dense and floats on top of water. The correct answer to the student's question is B) It separates into layers.
Step-by-step explanation:
When oil is mixed with water, the two substances do not mix uniformly. According to Figure 15.6.1, when water and oil are combined, they form separate layers because the nonpolar oil molecules will not dissolve into the polar water molecules. The result is that oil, being less dense than water, forms a top layer above the water. This is a physical manifestation of the principle that water and oil are immiscible. Therefore, in answering the student's question, the correct option is B) It separates into layers. Olive oil, in particular, as it cools, will slowly solidify over a range of temperatures, but this solidification occurs separately from its interaction with water. As for the changes of state, Figure 6.1.4 indicates that a liquid can evaporate into a gas or freeze into a solid, but in the context of the oil-water mixture, the primary behavior we're concerned with is the separation into distinct layers. When heated, components of a mixture can also separate based on differences in boiling points, as in distillation, but this is not relevant to the immediate question concerning what happens when oil is mixed with water at standard conditions.