Which region of nephron is impermeable to water but permeable to electrolytes?

Ascending limb of Henle’s Loop.

The correct answer is Option (1) -Ascending limb of Henle’s Loop.

Reabsorption is minimum in  ascending limb of Henle’s Loop. However, this region plays a significant role in the maintenance of high osmolarity of medullary interstitial fluid. The descending limb of loop of Henle is permeable to water but almost impermeable to electrolytes. This concentrates the filtrate as it moves down. The ascending limb is impermeable to water but allows transport of electrolytes actively or passively. Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the medullary fluid.