Here's why:

* Heterogeneous Mixture: A mixture where the components are not evenly distributed and can be easily distinguished.

* Water and Oil: Water is polar (meaning it has a positive and negative end) and oil is non-polar (meaning it has no distinct positive or negative ends). These differences in polarity prevent them from mixing.

* Separation: If you leave the container undisturbed, the oil will float on top of the water because it is less dense.

Let me know if you have any other science questions!