Homonym: oil and water (Incompatibility)
Oil and water are two common liquids that do not mix well. This is because oil is less dense than water and has a different molecular structure. When combined, oil forms droplets that float on the surface of water instead of blending in.
The reason for this separation lies in the concept of polarity. Water molecules are polar, meaning they have a positive and negative end, while oil molecules are non-polar. This difference prevents them from forming a homogeneous mixture, leading to the familiar sight of oil floating on top of water.