**Core Concept**
Intravenous potassium chloride can cause life-threatening cardiac arrhythmias, including ventricular fibrillation, due to the rapid shift of potassium ions into cardiac cells, which disrupts the electrical activity of the heart.

**Why the Correct Answer is Right**
The first line of treatment for ventricular fibrillation is defibrillation, which involves the delivery of an electric shock to restore a normal heartbeat. This is because ventricular fibrillation is a type of cardiac arrest, and immediate restoration of a perfusing rhythm is essential to prevent brain death and other complications. Defibrillation is typically performed using a defibrillator, which delivers a synchronized or unsynchronized shock to the heart, depending on the patient's situation.

**Why Each Wrong Option is Incorrect**
**Option A:** Administration of calcium chloride is incorrect because, while it can help stabilize cardiac membranes, it does not address the underlying cause of ventricular fibrillation.
**Option B:** Use of atropine is incorrect because atropine is typically used to treat bradycardia or asystole, not ventricular fibrillation.
**Option C:** Administration of magnesium sulfate is incorrect because, while magnesium can help stabilize cardiac membranes, it is not the first line of treatment for ventricular fibrillation.

**Clinical Pearl / High-Yield Fact**
In cases of suspected potassium chloride-induced cardiac arrest, it is essential to immediately stop the potassium infusion and prepare for defibrillation.

**Correct Answer: C. Administration of magnesium sulfate is incorrect because, while magnesium can help stabilize cardiac membranes, it is not the first line of treatment for ventricular fibrillation.**