Gas that diffuses fastest across alveolar membrane is:
Correct option is D, N2O. In Respiratory System; Exchange of Gases, the accurate description is N2O, and that is what you should commit to memory. Keep the definition tight and the role clear — N2O is the option that correctly names the structure, process, or principle asked for in Respiratory System; Exchange of Gases. Then N2O 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 N2O.
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.