Final answer:
A total of six leads are recorded from the four extremity electrodes by using the bipolar limb leads I, II, and III along with the augmented limb leads aVR, aVL, and aVF in a standard 12-lead ECG.
Step-by-step explanation:
When using a standard 12-lead electrocardiogram (ECG), the electrical activity of the heart is monitored through various leads. Specifically, four electrodes are placed on the extremities: one on each limb. The standard 12-lead ECG includes leads I, II, and III, which are derived from the potential differences between the limb electrodes. These three leads are known as the bipolar limb leads. Additionally, there are three augmented limb leads aVR, aVL, and aVF, which are also derived from the same four extremity electrodes. Therefore, in total, six leads (the three bipolar limb leads and the three augmented limb leads) are recorded from the four extremity electrodes.