Imbibition process involves
A. Both diffusion and capillary action
B. Only diffusion
C. Only capillary action
D. None of the above

Hint: One of the special types of diffusion that takes place when water is absorbed by solid colloids which then causes an increase in volume is known as imbibition. The absorption of water by seeds and dry wood are examples of imbibition. The seedlings would not be able to emerge from soil if there is no pressure due to imbibition. For imbibition to occur, a gradient between the absorbent and the liquid is essential.

Complete answer:
Option A. Both diffusion and capillary action: A type of diffusion in which the water is absorbed by the solid particles called colloids, which causes an enormous increase in volume, is known as imbibition. The process of imbibition involves movement of water into imbibant through adsorptive as well as capillary action.
Hence option A is the correct answer.
Option B. Only diffusion: The movement of a substance from a high concentration area to an area of low concentration is known as diffusion. Although imbibition is a special type of diffusion, the process of imbibition also includes capillary action.
Hence option B is not correct.
Option C. Only capillary action: The process of a liquid to flow through narrow spaces without the assistance of, or even in opposition to, external forces like gravity is known as capillary action. Imbibition is a special type of diffusion which also includes capillary action, and it is not only due to capillary action. Hence option C is not correct.
Option D. None of the above: Since option A is already correct.
So, option D is wrong.

Hence, option A. Both diffusion and capillary action is the correct answer.

Note:
The solid substances involved in the process of imbibition are referred to as Imbibant and the imbibed liquid is referred to as imbibate. For example, in the absorption of water by seed or dry wood, water is an imbibe and seed or dry wood is imbibant. In different imbibant, the capacity of imbibing will be different. For instance, if we consider proteins, which is a hydrophilic colloid, it will have maximum imbibing capacity.