Repolarization is the restoration phase, characterized by potassium leaving the cell and chloride entering the cell. Which option best describes this process?

• A. Potassium leaving the cell and chloride entering the cell
• B. Sodium entering the cell
• C. Chloride leaving the cell
• D. Calcium entering the cell

Answer: (A)

Repolarization is the phase where the cell returns to its resting negative membrane potential after depolarization. The central event is potassium channels opening and potassium moving out of the cell, which makes the interior more negative. The description here pairs potassium leaving with chloride entering. Potassium efflux is the defining feature of repolarization, so this captures the key mechanism. Chloride entering can influence membrane potential and reinforce hyperpolarization in some contexts, but it is not the primary driver of repolarization. The other possibilities describe depolarization or non-primary mechanisms (sodium entering drives depolarization; calcium entering occurs in other contexts and phases; chloride leaving would not align with the typical repolarization process).