A : Root pressure is dynamic and is always a positive hydrostatic pressure .
R : It is universal phenomenon and develops under absorption lag.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

### Step-by-Step Text Solution:

1. **Understanding Root Pressure**:
- Root pressure is defined as the positive hydrostatic pressure that develops in the xylem of roots. It is caused by the accumulation of water absorbed by the roots, particularly during the night when transpiration rates are low.

2. **Assertion Analysis**:
- The assertion states that "Root pressure is dynamic and is always a positive hydrostatic pressure." This is true because root pressure does fluctuate based on the water absorption and the turgidity of the root cells.

3. **Reason Analysis**:
- The reason states that "It is a universal phenomenon and develops under absorption lag." While root pressure can occur in many plants, the claim that it develops under absorption lag is incorrect. Absorption lag refers to a decrease in the rate of water absorption compared to transpiration, which does not lead to the development of root pressure.

4. **Conclusion**:
- Since the assertion is true and the reason is false, we conclude that the correct answer is that the assertion is true but the reason is false.

### Final Answer:
- Assertion is true, but reason is false.

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