Attractive forces between fluid molecules The tendency of molecules within the same fluid to attract each other is known as:

Introduction / Context:
Molecular forces govern many interfacial and bulk fluid phenomena. Distinguishing cohesion and adhesion is vital for understanding capillarity, wetting, droplet formation, and surface tension.

Given Data / Assumptions:

• Simple liquids, no complex surfactant effects.
• Standard definitions from fluid mechanics and physical chemistry.

Concept / Approach:
Cohesion refers to attraction between like molecules (e.g., water–water). Adhesion refers to attraction between unlike molecules (e.g., water–glass). Surface tension is a macroscopic manifestation of cohesive forces at an interface. Capillary action results from the interplay between adhesion (liquid–solid) and cohesion (liquid–liquid) plus gravity.

Step-by-Step Solution:

Verification / Alternative check:
Contact-angle behavior: water wets clean glass (adhesion > cohesion at interface), mercury does not (cohesion dominates), illustrating the concepts.

Why Other Options Are Wrong:

• Capillarity is the consequence of cohesion and adhesion in small tubes.
• Surface tension is a bulk effect of cohesive forces across an interface, not the fundamental inter-molecular attraction name.
• Adhesion describes unlike molecules.

Common Pitfalls:
Using “surface tension” interchangeably with “cohesion”; ignoring the role of adhesion in wetting.

Final Answer:
cohesion