Which ECG limb lead represents the right leg?

The correct answer is that Lead N represents the right leg. In the standard 12-lead ECG configuration, the limb leads are positioned to measure the electrical activity of the heart from different angles. Typically, the right leg is designated as the ground lead in the standard limb lead configuration but does not have a specific lead assigned to it for every recording.

Lead I, Lead II, and Lead III are the standard bipolar limb leads, which are derived from the voltage differences between pairs of limbs. Lead I measures the potential difference between the right arm and left arm, Lead II measures between the right arm and left leg, and Lead III measures between the left arm and left leg. None of these leads specifically represent the right leg on their own.

Lead N, referring to the negative lead associated with the right leg (or a hypothetical labeling in some contexts), effectively serves to represent that limb in certain setups by acting as a reference for measurements taken between the other limbs. Therefore, it is correct to identify Lead N as the lead that represents the right leg in this context.