Which statement about electrode counts for a 12-lead ECG is true?

• A. It uses 8 electrodes
• B. It uses 10 electrodes
• C. It uses 12 electrodes
• D. It uses 6 electrodes

Answer: (B)

A standard 12-lead ECG achieves twelve views of the heart’s electrical activity using ten physical electrodes: four placed on the limbs and six placed on the chest. The right-leg electrode serves as a ground reference and isn’t used to measure the leads. Leads I, II, and III come from the differences between the limb voltages, the augmented limb leads (aVR, aVL, aVF) are derived from those same limb voltages, and the chest leads V1–V6 are measured directly from the chest electrodes. So you get twelve leads without needing twelve physical sensors. The other counts don’t fit because eight electrodes wouldn’t provide enough sites to form all the standard vector views, twelve would be more than needed, and six would miss the limb-derived leads entirely.