The force of attraction between molecules of the same substance is

Step 1: Analyze the question The question asks for the name of the force of attraction between molecules of the same substance. The key words are "same substance."

Step 2: Explain the concepts

• Cohesion: the force of attraction between molecules of the same substance (e.g., water molecules attracting other water molecules).
• Adhesion: the force of attraction between molecules of different substances (e.g., water molecules sticking to glass).
• Surface tension: the property of a liquid surface behaving like a stretched elastic skin. It is a result of cohesive forces, but it is not the force itself.
• Capillarity: the rise or fall of a liquid in a narrow tube. It results from the interplay of cohesion and adhesion.

Step 3: Solve

• A. Cohesion: same-substance attraction ✔
• B. Capillarity: an effect, not a force between molecules ✘
• C. Adhesion: attraction between different substances ✘
• D. Surface tension: an effect caused by cohesion ✘

Step 4: Answer The correct option is A. cohesion.

Exam tip: Think "Cohesion = Company of the same kind" (like with like), while "Adhesion = adds on to something different" (like glue sticking to a surface). Mercury forming round droplets is cohesion at work, and water climbing up the side of a glass tube is adhesion.