Final answer:
The depolarization of the atria on an ECG is represented by the P wave, which is followed by the larger QRS complex and the T wave.
Step-by-step explanation:
The depolarization of the atria is an electrical event that is represented on the electrocardiogram (ECG) tracing by the P wave.
This small wave occurs as the atria contract, pushing blood into the ventricles. It is followed by the QRS complex, which represents ventricular depolarization, and the T wave, which denotes ventricular repolarization. The repolarization of the atria occurs during the QRS complex and is not visible because it is masked by the stronger electrical activity of the ventricles.