Root pressure is a

Options

A. Negative pressure
B. Positive pressure
C. Positive as well as negative depends upon external humidity level
D. Equal to atmospheric pressure

Answer

### Step-by-Step Solution

1. **Understanding Root Pressure**:
- Root pressure is a phenomenon that occurs in plants, specifically in the roots. It is the pressure exerted by the fluid (water and dissolved minerals) within the xylem vessels of the roots.

2. **Analyzing Options**:
- The question presents multiple choice options regarding the nature of root pressure. We need to evaluate each option to determine which one correctly describes root pressure.

3. **Evaluating Option 1 (Negative Pressure)**:
- The first option states that root pressure is negative. This is incorrect because root pressure is characterized by the accumulation of water and solutes, leading to a positive pressure within the xylem.

4. **Evaluating Option 2 (Positive Pressure)**:
- The second option claims that root pressure is positive. This is correct. Root pressure results from the active transport of ions from the soil into the root cells, which causes water to move into the roots, creating a positive pressure in the xylem.

5. **Evaluating Option 3 (Positive and Negative)**:
- The third option suggests that root pressure can be both positive and negative depending on external humidity levels. This is misleading. While environmental factors can influence water movement, root pressure itself is primarily a positive pressure phenomenon.

6. **Evaluating Option 4 (Equal to Atmospheric Pressure)**:
- The fourth option states that root pressure is equal to atmospheric pressure. This is also incorrect, as root pressure is generally greater than atmospheric pressure when it is present.

7. **Conclusion**:
- After evaluating all the options, the correct answer is **Option 2: Positive Pressure**.