The correct answer to the question is option 3: Absorption. The process of imbibition refers to the absorption of a liquid by a solid, particularly the swelling and uptake of a liquid by a permeable substance such as a cell wall or a porous material.

Option 1: Diffusion can also occur during the process of imbibition, but it is not the main process involved. Diffusion refers to the movement of molecules from an area of higher concentration to an area of lower concentration, and it can play a role in the spreading of the absorbed liquid through the solid material.

Option 2: Capillary action is not directly related to the process of imbibition. Capillary action refers to the ability of a liquid to flow against gravity in a narrow tube or space due to the adhesive and cohesive forces between the liquid and the tube or space.

Option 4: Both diffusion and capillary action may occur during imbibition, but the primary process in imbibition is absorption. So, option 4 is incorrect.

In conclusion, imbibition primarily involves absorption, with diffusion and capillary action potentially playing a secondary role.