Assertion. Primary xylem is exarch in roots and endarch in stems.
Reason. Exarch condition of xylem facilitates inflow of water from cortex whereas endarch condition favours ascent of sap

Options

A. If both Assertion and Reason are true and the Reason is a correct explanation of the Assertion
B. If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion
C. If Assertion is true but the Reason is false
D. If both Assertion and Reason are false

Answer

To solve the question, we need to analyze the assertion and reason provided, and determine their validity and relationship.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Primary xylem is exarch in roots and endarch in stems."
- **Exarch** means that the protoxylem (the first-formed xylem) is located towards the outside, while the metaxylem (the later-formed xylem) is located towards the inside. This is typical in roots.
- **Endarch** means that the protoxylem is located towards the inside and the metaxylem is towards the outside, which is typical in stems.

2. **Understanding the Reason**:
- The reason states that "Exarch condition of xylem facilitates inflow of water from cortex whereas endarch condition favours ascent of sap."
- In roots, the exarch arrangement allows for efficient absorption of water from the surrounding soil and cortex into the xylem.
- In stems, the endarch arrangement supports the upward movement of water (ascent of sap) to the leaves and other parts of the plant.

3. **Evaluating the Truth of the Statements**:
- Both the assertion and the reason are true based on the definitions and functions of xylem in roots and stems.
- The reason correctly explains why the xylem is arranged in these specific ways in roots and stems.

4. **Conclusion**:
- Since both the assertion and reason are true, and the reason provides a correct explanation for the assertion, we conclude that the answer is that both statements are true and the reason is a correct explanation of the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason is a correct explanation of the assertion.