The answer is oil. Oil has a lower density than water, which is why it floats on the surface when the two are mixed.
To understand why oil is less dense, we need to look at the molecular structure of both substances. Water is a polar molecule, meaning it has a positive and negative end. This allows water molecules to form hydrogen bonds with each other, creating a denser structure. The density of water is approximately 1 gram per cubic centimeter at room temperature.
On the other hand, most oils are made up of long chains of carbon and hydrogen atoms, which do not form hydrogen bonds like water. The molecular structure of oil is less compact than that of water. As a result, most oils have densities that range from about 0.8 to 0.9 grams per cubic centimeter, which makes them lighter than water.
This difference in density is also why you often see oil floating on the surface of water in various scenarios, whether it’s in cooking or environmental spills. Understanding this property can be useful in many applications, from cooking to environmental science.