The phenomenon of a liquid wetting a solid surface, like water wetting a glass tube, is governed by the interplay of two primary types of intermolecular forces: cohesion and adhesion.

Wetting Fundamentals: Cohesion and Adhesion

To understand why water wets the surface of a glass tube, it's essential to define cohesion and adhesion:

• Cohesion: This refers to the attractive forces between molecules of the same substance. For example, water molecules are attracted to other water molecules. This force is responsible for phenomena like surface tension and the tendency of water to form droplets.
• Adhesion: This refers to the attractive forces between molecules of different substances. In the context of the question, it's the attraction between water molecules and the molecules of the glass tube.

When a liquid comes into contact with a solid surface, the balance between these two types of forces determines whether the liquid will wet the surface or not.

Water Wetting Glass Explained

For wetting to occur, the adhesive forces between the liquid and the solid must be stronger than the cohesive forces within the liquid itself. Specifically, for water in a glass tube:

• Water molecules are strongly attracted to the molecules that make up glass (these are the adhesive forces).
• While water molecules also attract each other (these are the cohesive forces), the attraction between water and glass is significantly stronger than the attraction between water molecules themselves.

Because the adhesion between water and glass is greater than the cohesion within water, the water molecules are pulled towards and spread out on the glass surface. This causes the water to "wet" the tube. This strong adhesion is also responsible for the concave meniscus that water forms in a glass tube and for the phenomenon of capillary action, where water appears to climb the walls of the tube.

Analyzing Options for Water in a Glass Tube

Let's evaluate each provided option based on our understanding of cohesion and adhesion in relation to water wetting a glass tube:

• More cohesion of water molecules: If the cohesive forces among water molecules were stronger than the adhesive forces to glass, water would tend to pull away from the glass and form droplets. This would result in non-wetting, which is the opposite of what is observed. Therefore, this option is incorrect.
• Adhesion between water is glass is less: If the adhesive forces between water and glass were weaker (less) than the cohesive forces of water, the water would not wet the glass. Instead, it would pull away from the glass surface, leading to non-wetting. This contradicts the observation that water wets glass. Therefore, this option is incorrect.
• Density of glass is more than water: While it is true that the density of glass is generally greater than water, this physical property has no direct influence on why water wets the surface of the glass tube. Wetting is governed by intermolecular forces, not density differences. Therefore, this option is incorrect.
• Adhesion between water is glass is more: This option correctly identifies the reason. When the attractive forces between water molecules and glass molecules (adhesion) are stronger than the attractive forces among water molecules themselves (cohesion), water spreads out and adheres to the glass surface, causing it to "wet" the tube. This directly explains the observed phenomenon. Therefore, this option is correct.

In summary, the key reason water wets the surface of a glass tube is that the adhesive forces between water and glass molecules are stronger than the cohesive forces within the water itself.