Which one among the following does not wet the walls of the glass vessel in which it is kept ?

Wetting is determined by the balance between adhesive forces (between liquid and solid) and cohesive forces (within the liquid). Water and alcohol wet glass because their adhesive forces with glass are stronger than their internal cohesive forces, resulting in a contact angle less than 90 degrees. Specifically, water wets glass due to strong adhesion. In contrast, mercury does not wet glass because its cohesive forces are significantly larger than its adhesive forces with the glass surface. This leads to an obtuse contact angle (approximately 135 to 138 degrees), causing the mercury to form droplets and depress in a capillary tube rather than spreading or 'wetting' the vessel walls. Phenol, while it may decrease the surface tension of water, is generally considered a wetting agent in various chemical contexts. Therefore, mercury is the only substance listed that consistently avoids wetting glass.