**Core Concept**
The normal QRS axis in electrocardiography (ECG) refers to the orientation of the electrical activity of the heart in the frontal plane. It is a crucial parameter in interpreting ECG tracings, as it can indicate various cardiac conditions. The normal QRS axis typically ranges between -30° and +100°.

**Why the Correct Answer is Right**
The QRS axis is determined by the direction of the electrical impulse as it travels through the ventricles. Normally, the impulse originates from the right bundle branch and travels towards the left ventricle. This results in a positive QRS complex in leads I, II, and III, and a negative QRS complex in lead aVR. The normal QRS axis is influenced by the anatomical position of the heart in the chest and the orientation of the ventricles. In a normal individual, the QRS axis is typically between -30° and +100°, with an average of around +90°.

**Why Each Wrong Option is Incorrect**
**Option A:** A QRS axis of -150° would indicate a left axis deviation, which is abnormal and often associated with conditions such as Wolff-Parkinson-White syndrome or left ventricular hypertrophy.
**Option B:** A QRS axis of 180° would indicate a right axis deviation, which is also abnormal and often associated with conditions such as right ventricular hypertrophy or a posterior myocardial infarction.
**Option C:** A QRS axis of 0° would indicate a horizontal QRS axis, which is also abnormal and often associated with conditions such as left ventricular hypertrophy or a left bundle branch block.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the QRS axis can be influenced by various factors, including the patient's posture, respiration, and body habitus. Therefore, it's crucial to consider these factors when interpreting ECG tracings.

**Correct Answer: A. -30° to +100°**