Assertion: In the descending limb of loop of Henle the urine is hypotoonic, while in ascending limb of loop of Henle, the urine is hypertonic.
Reason: Descending limb is impermeable to water while ascending limb is impermeable to `Na^(+)`

Options

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

Answer

D

Explanation

The descending limb of loop of henle is permeable to water but almost impermeable to electroytes. This concentrates the filtrate as it moves down. The ascending limb is impermeable to water but allows transport of electrolytes actively or passivly. Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the medullary fluid.