Illuviation is the process of

Correct option is A

The correct answer is (A) Accumulation

Explanation:
• In soil science, Illuviation is the process of accumulation of soil material (such as clay, iron, aluminum, or organic matter) in a lower soil horizon.
• This material is typically washed down from the upper horizons (A or E) by the downward movement of water.
• The horizon where this accumulation occurs is called the Illuvial Horizon (generally the B horizon).
• This is a fundamental pedogenic process that leads to the development of distinct sub-surface characteristics, such as the formation of an Argillic (clay-rich) or Spodic (metal/humus-rich) horizon.

Information Booster:
• Eluviation (spelled with an 'E') is the opposite: the removal or leaching of materials from a horizon. Think 'E' for Exit and 'I' for In.
• The combination of eluviation and illuviation is sometimes called "lessivage."
• Illuviation is most prominent in humid climates where there is enough rainfall to move materials through the soil profile.

Additional Knowledge:
• Leaching (Option B): The overall process of dissolving and carrying nutrients and minerals downward; it is the cause of eluviation.
• Transportation (Option C): The movement of particles, which is part of the illuviation process, but "accumulation" is the specific defining outcome of illuviation.
• Weathering (Option D): The physical or chemical breakdown of rocks and minerals into smaller particles; it provides the material that eventually becomes subject to illuviation.