Final answer:
The P wave on an ECG reflects atrial depolarization. The QRS complex indicates ventricular depolarization, while the T wave represents ventricular repolarization. Atrial repolarization is masked by the QRS complex and is not seen on an ECG.
Step-by-step explanation:
The correct answer to the question about the electrocardiogram (ECG) components is that the P wave reflects the depolarization of the atria of the heart.
When an ECG is performed, the P wave is the first waveform that appears and it represents atrial depolarization, which is essentially the electrical activation that precedes the contraction of the heart's atria.
Just after the start of the P wave, the atria begin contracting. The QRS complex follows the P wave, and it indicates the depolarization of the ventricles, which is a larger and more complex signal due to the size and function of the ventricles.
Subsequent to the QRS complex, the T wave shows the repolarization of the ventricles. It's also important to note that the repolarization of the atria takes place during the QRS complex and is not visible on the ECG because it is masked by the ventricular depolarization.