Acquisition of ECG signals using biomedical systems

Which of the following indicates atrioventricular conduction delay in an ECG?
Why is the QRS complex narrower and sharper compared to the P wave?
What part of the heart’s conduction system delays signal transmission to allow ventricular filling?
If you observe 50 Hz noise in an ECG signal during acquisition, the most probable cause is:
In a 3-lead ECG, what is the role of the RL electrode?