Which part of nephron is impermeable to water?
Correct option is B, Thick ascending limb. In Excretory System, the accurate description is Thick ascending limb, and that is what you should commit to memory. Keep the definition tight and the role clear — Thick ascending limb is the option that correctly names the structure, process, or principle asked for in Excretory System. Then Thick ascending limb is the answer you can defend. Check yourself by covering the options and writing the answer first, then matching the letter — that builds confidence. If the wording feels dense, translate it into everyday language first, then map that plain sentence back onto Thick ascending limb.
Ref: Animal physiology is Unit 7 of the CSIR NET Life Science Syllabus, covering core body systems. It accounts for roughly 10% of the total marks in Sections B and C.