The action of blotting paper on ink is due to

1. Analyze the question The question asks which physical phenomenon explains how blotting paper soaks up ink.

2. Explain the concept Blotting paper is made of cellulose fibres with many tiny gaps (pores) between them. These gaps act like very thin tubes. Capillarity (capillary action) is the rise or movement of a liquid through narrow tubes or pores. It happens because of two forces:

• Adhesion: attraction between the liquid molecules and the walls of the pores.
• Cohesion: attraction between the liquid molecules themselves.

When adhesion is stronger than cohesion, the liquid is pulled into the narrow spaces.

3. Solution, step by step

• Ink touches the blotting paper.
• The ink molecules are attracted to the cellulose fibres (adhesion).
• The liquid is drawn up through the tiny pores between the fibres.
• The paper therefore absorbs the ink.

Checking the other options:

• A. Diffusion: the spreading of particles from high to low concentration. It is not the main cause of ink being drawn into paper.
• B. Osmosis: movement of water through a semi-permeable membrane. Blotting paper is not acting as one.
• D. Surface tension: this is related to capillarity, but it is a property of the liquid's surface. It is not the direct action of liquid moving through pores.

4. Answer The action of blotting paper on ink is due to capillarity, which is option C.

5. Exam tip Link everyday examples to capillarity:

• blotting paper absorbing ink
• a wick drawing up kerosene in a lamp
• water rising in plant stems
• a towel soaking up water

If the question involves liquids moving through tiny spaces, think "capillarity".