When completing the water properties lab, which property of water was responsible for the water molecules sticking to the penny?

Adhesion.

Explanation:

Water molecules exhibit the properties of cohesion and adhesion. Adhesion refers to the property of water molecules to stick to some other substance while cohesion is the property of water molecules to stick together. Hence, sticking of water molecules to the penny is example of adhesion where water molecules are attracted towards the penny.