Beta waves are commonly seen during:
Correct option is C, Active mental work. In Structure and Function of Nervous System, the accurate description is Active mental work, and that is what you should commit to memory. Keep the definition tight and the role clear — Active mental work is the option that correctly names the structure, process, or principle asked for in Structure and Function of Nervous System. Then Active mental work 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 Active mental work.
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.