Difficulty: Easy
Correct Answer: Because water adheres strongly to glass (adhesion > cohesion), while mercury's cohesion > adhesion to glass
Explanation:
Concept
A liquid spreads when adhesion to the surface exceeds cohesion; it beads up when cohesion dominates or surface tension is very high.
Application
Water–glass: strong adhesion ⇒ wetting/spreading. Mercury: very high surface tension and strong cohesion with weak adhesion to glass ⇒ spherical drops (non-wetting).
Final Answer
Because water adheres strongly to glass (adhesion > cohesion), while mercury's cohesion > adhesion to glass
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