During the countercurrent multiplication in the loop of Henle, which segment is impermeable to water but actively transports salts?
Correct: C
The ascending limb of the loop of Henle is impermeable to water and actively transports Na⁺ and Cl⁻ out of the filtrate via secondary active transport. The descending limb is water-permeable but not salt-reabsorbing, while the PCT and DCT have different reabsorption roles.