Arrange the following rock particles which occur in soil in the increasing order of their sizes (keeping the smallest one first) :
Sand, Clay, Gravel, Silt.

Answer

To arrange the rock particles in soil in increasing order of their sizes, we need to identify the size of each particle type: Clay, Silt, Sand, and Gravel.

### Step-by-Step Solution:

1. **Identify the smallest particle**:
- **Clay** is the smallest of the four types of particles. It consists of very fine particles that are less than 0.002 mm in diameter.

2. **Next size up**:
- **Silt** comes next. Silt particles are larger than clay but smaller than sand, typically ranging from 0.002 mm to 0.05 mm in diameter.

3. **Larger particles**:
- **Sand** is larger than silt. Sand particles range from 0.05 mm to 2 mm in diameter.

4. **Largest particle**:
- **Gravel** is the largest of the four. Gravel particles are larger than 2 mm in diameter.

### Final Arrangement:
Putting it all together, the increasing order of the rock particles based on their sizes is:
**Clay < Silt < Sand < Gravel**