Concept:Capillarity is the rise or movement of a liquid inside narrow spaces or tubes.
Explanation:Blotting paper contains many tiny pores or narrow channels.
When ink touches blotting paper, the adhesive force between the ink and the paper fibres is stronger than the cohesive force between the ink molecules.
This causes the ink to enter and move up through the tiny pores of the paper.
This spontaneous movement of a liquid in narrow spaces is known as capillarity or capillary action.
Diffusion involves the mixing of particles, osmosis needs a semi-permeable membrane, and surface tension only affects the liquid surface.
For this reason, blotting paper absorbs ink primarily because of capillarity.
Answer:C. Capillarity