Final answer:
In the aVF lead of an ECG, the positive electrode is attached to the left leg (LL).
Step-by-step explanation:
The limb that is positive in the aVF lead is the left leg (LL). During an electrocardiogram (ECG), electrodes are placed on the patient's limbs and chest to measure the heart's electrical activity. The aVF lead specifically measures the electrical potential difference between the left leg and the combined potential from the right arm and left arm, with the left leg electrode being the positive electrode. The measurement from this lead gives information about the heart's electrical activity in the inferior plane.