Capillary action is best described as:

Capillary action is best described as:

• A. The combined force of cohesion and adhesion that causes liquid to rise in narrow tubes
• B. The diffusion of molecules through a membrane
• C. The vaporization of a liquid at its boiling point
• D. The mixing of two immiscible liquids

Answer: (A)

Capillary action arises from the interplay of cohesive forces within the liquid and adhesive forces between the liquid and the tube walls, aided by surface tension at the liquid–air interface. When the liquid wets the wall, adhesive forces pull the liquid up along the surface and cohesive forces hold the rest of the liquid column together, producing a rise in a narrow tube. The height of the rise depends on surface tension, the liquid’s density, gravity, the tube radius, and the contact angle, with smaller radii and better wetting increasing the rise (roughly h ∝ cos θ / r). If the liquid does not wet the surface well, the liquid may be drawn down rather than up. This phenomenon is distinct from diffusion through a membrane, vaporization at the boiling point, or mixing of immiscible liquids, which involve different mechanisms.

Capillary action arises from the interplay of cohesive forces within the liquid and adhesive forces between the liquid and the tube walls, aided by surface tension at the liquid–air interface. When the liquid wets the wall, adhesive forces pull the liquid up along the surface and cohesive forces hold the rest of the liquid column together, producing a rise in a narrow tube. The height of the rise depends on surface tension, the liquid’s density, gravity, the tube radius, and the contact angle, with smaller radii and better wetting increasing the rise (roughly h ∝ cos θ / r). If the liquid does not wet the surface well, the liquid may be drawn down rather than up. This phenomenon is distinct from diffusion through a membrane, vaporization at the boiling point, or mixing of immiscible liquids, which involve different mechanisms.