Capillarity is the phenomenon of a liquid rising or falling in a narrow tube due to the combined effects of surface tension, cohesion, and adhesion. It occurs when the cohesive forces between liquid molecules are greater than the adhesive forces between the liquid and the tube. Let's discuss each of the factors involved in capillarity in detail.

1. Surface tension:
Surface tension is the force exerted by the surface of a liquid that tends to minimize its surface area. It is caused by the cohesive forces between the liquid molecules. In the case of capillarity, surface tension plays a crucial role. When a capillary tube is dipped into a liquid, the liquid rises or falls in the tube to minimize the surface area exposed to air. The surface tension creates an upward force that pulls the liquid up into the tube.

2. Cohesion:
Cohesion is the attractive force between molecules of the same substance. In the case of liquid, it refers to the attraction between liquid molecules. Cohesion is responsible for the formation of the meniscus, which is the curved surface of a liquid in a capillary tube. The cohesive forces between liquid molecules pull the liquid upward, causing it to rise in the capillary tube.

3. Adhesion:
Adhesion is the attractive force between molecules of different substances. In the case of capillarity, adhesion refers to the attraction between the liquid molecules and the walls of the capillary tube. Adhesion helps the liquid to wet the walls of the tube, allowing it to rise or fall. If the adhesive forces are stronger than the cohesive forces, the liquid will rise in the tube. If the cohesive forces are stronger, the liquid will fall.

4. Vapour pressure:
Vapor pressure is the pressure exerted by the vapor of a liquid in equilibrium with the liquid phase at a given temperature. It is related to the tendency of molecules to escape from the liquid phase and enter the vapor phase. While vapor pressure does not directly cause capillarity, it can affect the height to which a liquid rises in a capillary tube. A lower vapor pressure may result in a higher rise in the tube due to reduced evaporation from the meniscus.

5. Weight density of liquid:
Weight density, also known as density, is the mass of a substance per unit volume. While weight density does not directly cause capillarity, it is related to the gravitational force acting on the liquid. The weight of the liquid in the capillary tube can counteract the upward capillary force, affecting the height to which the liquid rises.

In conclusion, capillarity is primarily due to surface tension, cohesion, and adhesion. Surface tension and cohesion create an upward force that pulls the liquid into the capillary tube, while adhesion helps the liquid to wet the walls of the tube. Vapour pressure and weight density of the liquid can also influence the height to which the liquid rises.