Answer : 2. "Humus"
Explanation :

The decayed remains of living organisms in soil are called (B) Humus. Humus is the organic material that forms as a result of the decomposition of plant and animal matter. It is a dark, nutrient-rich component of soil and plays a vital role in soil fertility. Humus improves soil structure, retains moisture, and provides essential nutrients for plant growth. It is a key element in sustaining healthy and productive soils in various ecosystems.