Atrial depolarization is represented by:

Explanation

The P wave on an electrocardiogram (ECG) represents atrial depolarization, which is the electrical activation that initiates the contraction of the atria. The QRS complex follows, representing ventricular depolarization, while the T wave represents ventricular repolarization. Therefore, the P wave is specifically associated with atrial depolarization. The term 'PQRS' is not a valid ECG component, thus it does not correspond to any specific physiological event in the heart.