The force of attraction between molecules of the same substance is called the force of cohesion. This force is lesser in liquids and least in gases.
The force of attraction between the molecules of the different substances is called the force of adhesion.
Real-life example: It is difficult to break a drop of mercury into small droplets because of the large cohesive force between the mercury molecules.
Real-life example: Adhesive force enables us to write on the blackboard with a chalk.
EXPLANATION:
When a water drop falls on the surface of the oil, two forces come into play i.e., the cohesion forces within the water molecules and the other is adhesion forces between oil and water.
As we know that oil is hydrophobic in nature, therefore, the adhesive forces between oil and water are much weaker compared to the cohesive forces between water and water.
Therefore, the water drop on the surface of oil has a tendency to maintain its spherical shape in order to minimize the surface energy.