Final answer:
The P wave on the ECG represents depolarization of the atria.
Step-by-step explanation:
The correct answer is c. P wave. The P wave on the electrocardiogram (ECG) tracing represents the depolarization of the atria. During this time, the atria are contracting and pumping blood into the ventricles. The QRS complex represents the depolarization of the ventricles, while the T wave represents the repolarization of the ventricles. The repolarization of the atria occurs during the QRS complex, which is why it is not visible on the ECG.