Equilibrium potential of an ion is defined as membrane potential at which:
Pick C: No net ion movement occurs. Thinking about Action potential in a practical way — what the structure does, or what the process achieves — leads you here. Clinically and academically, the same logic shows up again and again: this is mainly a definition check, and No net ion movement occurs is the standard term or meaning used in Action potential. Hence No net ion movement occurs is correct. Treat this as a building block for the rest of Action potential; neighbouring topics often reuse the same principle. Keep a one-line summary card for this idea and revisit it before the paper; short, repeated review beats long cramming sessions.
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.