Mercury does NOT wet glass because

Step 1: Analyze the question We are asked why mercury does not wet glass. "Wetting" describes whether a liquid spreads over and sticks to a solid surface.

Step 2: The concept Two forces matter here:

• Cohesive force: attraction between molecules of the same substance (mercury to mercury).
• Adhesive force: attraction between molecules of different substances (mercury to glass).

The balance between them decides how a liquid behaves:

• If adhesion > cohesion, the liquid clings to the surface and spreads. It wets the surface. Water on clean glass is an example. The meniscus curves upward (concave) and the angle of contact is acute.
• If cohesion > adhesion, the liquid molecules pull toward each other more than toward the surface. The liquid does not wet the surface and forms round droplets. The meniscus curves downward (convex) and the angle of contact is obtuse (about 140° for mercury on glass).

Step 3: Apply it to mercury Mercury atoms are strongly bonded to each other (metallic bonding), so its cohesive force is very large. Its attraction to glass is comparatively weak. Cohesion therefore exceeds adhesion, so mercury beads up into spherical droplets and rolls off glass without leaving a film. This is also why mercury has a convex meniscus in a glass tube, and why it is depressed (capillary depression) rather than rising in a narrow tube.

Step 4: Check the other options

• A. Being amorphous is a structural property of glass and does not explain wetting.
• B. This is the condition for wetting, the opposite of what happens with mercury.
• D. Thermal conductivity has nothing to do with wetting.
• E. Opacity is an optical property and is unrelated.

Answer: C. The cohesive force is greater than the adhesive force.

Exam tip: Remember "Water Adheres, Mercury Coheres." Water wets glass because adhesion wins. Mercury does not wet glass because cohesion wins. Mercury also shows a convex meniscus and capillary depression, which come up often in NECO and JAMB questions.