Blotting paper is able to soak up and absorb ink efficiently mainly due to which physical phenomenon acting in the tiny pores of the paper?

Introduction / Context:
When you place blotting paper on a wet ink spot, the paper quickly soaks up the ink. This everyday observation can be explained using basic fluid physics. The key concept is capillary action, which allows liquids to rise or move through narrow spaces without external forces. This question tests whether you can correctly identify capillary action as the main reason blotting paper works so effectively.

Given Data / Assumptions:

• Blotting paper is porous, with many tiny capillary like channels.
• Ink is a liquid that wets the paper, meaning it tends to spread on its surface.
• The absorption happens even against gravity to some extent.
• The options mention capillary action, diffusion, siphon action and viscosity.

Concept / Approach:
Capillary action occurs when adhesive forces between a liquid and the walls of a narrow tube, combined with surface tension, cause the liquid to rise or move in the tube. Blotting paper contains a network of fine pores that behave like many tiny capillary tubes. When the edge of the paper touches ink, the ink is drawn into these pores by capillary forces, allowing the paper to absorb the liquid efficiently. Diffusion involves random motion of molecules and is much slower and not the main mechanism here. Siphon action requires a continuous path and height difference, which is not the case. Viscosity is a measure of internal friction and would oppose flow if it were very high.

Step-by-Step Solution:
Step 1: Observe that blotting paper has a fibrous, porous structure with many tiny channels.Step 2: When the paper touches ink, the ink spreads into these pores and rises above the original level of ink.Step 3: Recognise that this upward or sideways movement of liquid into narrow pores is a characteristic of capillary action.Step 4: Understand that adhesive forces between ink and paper, together with surface tension, pull the ink into the pores.Step 5: Note that diffusion alone would be too slow and random to explain the rapid absorption observed.Step 6: Conclude that capillary action is the dominant phenomenon that allows blotting paper to absorb ink.

Verification / Alternative check:
Similar behaviour can be seen when you dip the corner of a paper towel into water; the water climbs up the towel against gravity. Classic experiments with thin glass tubes in water show the liquid rising to a certain height due to capillary action. These examples match the behaviour of blotting paper with ink and support the explanation that capillary forces in narrow pores are responsible.

Why Other Options Are Wrong:
Diffusion of ink molecules through the paper plays a minor role but is not the main driver of rapid bulk liquid movement into the pores. Siphon action requires a U shaped tube and flow driven by gravity difference in connected columns, which is not the setup here. High viscosity would actually slow the movement of ink rather than help it; low viscosity assists flow. Therefore, these options do not correctly describe the primary phenomenon.

Common Pitfalls:
Some students confuse diffusion with any spreading of a liquid and may choose that answer. Others might not be familiar with the term capillary action. To avoid this, remember that capillary action specifically refers to movement of liquids in narrow tubes or pores due to adhesive forces and surface tension, and blotting paper is a classic example of this effect.

Final Answer:
Blotting paper absorbs ink mainly because of capillary action acting in the fine pores of the paper.