* Density: Decane has a lower density than water. Density is a measure of how much mass is packed into a given volume.

* Immiscibility: Water and decane are immiscible, meaning they don't mix. When they are combined, they form two distinct layers.

* Buoyancy: The less dense substance (decane) will be less affected by gravity and will float on top of the denser substance (water).

Think of it like oil and water. Oil floats on water for the same reason.