Final answer:
The descending limb of the loop of Henle is permeable to water, while the ascending limb is permeable to sodium and chloride ions.
Step-by-step explanation:
In the loop of Henle, the permeability of the membrane changes. Specifically, the descending limb is permeable to water, allowing water to flow from the filtrate into the interstitial fluid, which increases the osmolality inside the limb. The ascending limb, conversely, is permeable to sodium ions (Na+) and chloride ions (Cl−), allowing these ions to exit the filtrate through ion channels and further up the limb, sodium is actively transported out of the filtrate, with chloride following passively. Thus, the descending and ascending limbs are permeable to water and sodium ions respectively.
The correct answer to the given question is option b) Descending: Water, Ascending: Sodium ions.