Explain why

Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)

Mercury molecules have strong forces of attraction between themselves (cohesive forces) and the forces of attraction between molecules of mercury and glass are weak (Adhesive forces).So they form a droplets on the glass surface.

Water molecules have weak forces of attraction between themselves (cohesive forces) and the forces of attraction between the water molecules and glass molecules is strong (adhesive forces). So water spreads on glass.