Which of the following best describes humus?

• A. Fresh leaf litter
• B. Water-soluble sugars
• C. Stable decomposed organic matter
• D. Mineral nutrients

Answer: (C)

Humus is the stable, decomposed organic matter in soil—that resistant residue left after organic material has been broken down by microbes and soil life and then stabilized so it persists for a long time. This material enriches soil by helping to hold water, improve soil structure, and support nutrient retention and slow release as it continues to decompose gradually. Fresh leaf litter is still undecomposed material, not stable, so it isn’t humus. Water-soluble sugars are quick‑moving carbon compounds that don’t persist in soil as a stable, structural component. Mineral nutrients are inorganic components, not organic matter, so they don’t describe humus.