A layer of soil profile is rich in

Options

A. minerals
B. humus
C. litter
D. none of these

Answer

### Step-by-Step Solution:

1. **Understanding Soil Profile**: The soil profile consists of different layers, each with distinct characteristics and compositions. The main layers include the O horizon, A horizon, B horizon, and C horizon.

2. **Identifying the O Horizon**: The topmost layer, known as the O horizon, is rich in organic matter such as decomposed leaves and twigs. This layer is crucial for the initial nutrient input into the soil.

3. **Analyzing the A Horizon**: Below the O horizon is the A horizon, which is also rich in organic material. This layer contains a significant amount of humus, which is formed from the decomposition of organic matter. Humus is vital for soil fertility as it enhances nutrient availability and improves soil structure.

4. **Examining the B Horizon**: The B horizon, or subsoil, lies beneath the A horizon. It is where minerals leached from the upper layers accumulate. While it does contain nutrients, it is not as rich in organic matter as the A horizon.

5. **Looking at the C Horizon**: The C horizon consists of weathered rock and parent material. It does not contain significant organic matter or humus.

6. **Conclusion**: Based on the characteristics of these layers, the A horizon is identified as the layer of soil profile that is rich in humus. Therefore, the correct answer to the question is that a layer of soil profile is rich in humus.

### Final Answer:
A layer of soil profile is rich in **humus**.