Assertion : In the descending limb of loop of Henle , the urine is hypertonic , while in ascending limb of loop of Henle , the urine is Hypotonic .
Reason : Descending limb is impermeable to Na' while ascending limb is impermeable to `H_(2)O`

Options

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

Answer

To solve the question, we need to analyze the assertion and reason provided regarding the loop of Henle in the nephron of the kidney.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states: "In the descending limb of the loop of Henle, the urine is hypertonic, while in the ascending limb of the loop of Henle, the urine is hypotonic."
- This is incorrect. In the descending limb, the urine becomes more concentrated (hypertonic) as water is reabsorbed, while in the ascending limb, the urine becomes diluted (hypotonic) as sodium ions are reabsorbed without water.

2. **Understanding the Reason**:
- The reason states: "The descending limb is impermeable to Na⁺ while the ascending limb is impermeable to H₂O."
- This statement is correct. The descending limb allows water to pass but not sodium ions, while the ascending limb allows sodium ions to be reabsorbed but does not allow water to pass.

3. **Evaluating the Relationship**:
- Since the assertion is false and the reason is true, we need to determine the correct option based on this evaluation.

4. **Conclusion**:
- The assertion is false, and the reason is true. Therefore, the correct answer is that the assertion is true and the reason is false.

### Final Answer:
The correct option is: "Assertion is false, Reason is true."