Fluid Properties MCQ with answer and solution

Concept

Mercury does not wet glass because the cohesive forces between mercury molecules are much stronger than the adhesive forces between mercury and glass.

Step-by-step solution

1. Understand the forces acting between liquid and solid surfaces. 2. Cohesion is the force of attraction between molecules of the same liquid. 3. Adhesion is the force of attraction between liquid molecules and molecules of a solid boundary (like glass). 4. When cohesive force is greater than adhesive force, the liquid does not wet the solid and forms a convex meniscus. Answer: (B) Adhesion

Explanation

Mercury droplets form spherical shapes and do not wet glass because internal cohesive forces dominate over adhesive forces between glass and mercury.

Why the other options are wrong

A: Cohesion is the property holding mercury molecules together, but the non-wetting behavior specifically relates to the relative weakness of adhesion compared to cohesion. C: Viscosity is the resistance to flow and has no direct effect on wetting. D: Surface tension is responsible for the spherical shape of droplets, but the wetting property depends on adhesive forces.

Shortcut

Remember: Water wets glass (Adhesion > Cohesion), but mercury does not wet glass (Cohesion > Adhesion).

Common mistake

Students often confuse cohesion and adhesion; cohesion is for same molecules, adhesion is for different molecules.