Final answer:
The active transport of NaCl in the ascending limb of loop of Henle leads to hyperosmotic fluid in the interstitial region.
Step-by-step explanation:
The active transport of NaCl in the ascending limb of loop of Henle leads to hyperosmotic fluid in the interstitial region. As the filtrate enters the ascending limb, sodium and chloride ions exit through ion channels. Further up, sodium is actively transported out of the filtrate, and chlorine ions follow. This creates a higher osmolarity in the interstitial region.