Step 1: Understanding the process.
Leaching is the process by which water percolates through the soil and carries soluble inorganic nutrients downward, away from the root zone.
Step 2: Analyzing the options.
(A) Fragmentation: Incorrect — It is the breakdown of detritus into smaller pieces by detritivores.
(B) Leaching: Correct — The downward movement of soluble nutrients is called leaching.
(C) Catabolism: Incorrect — It is the breakdown of organic molecules inside cells.
(D) Humification: Incorrect — It refers to the formation of humus from decomposed organic matter.
Step 3: Conclusion.
The correct term for downward movement of soluble nutrients is Leaching.