**Core Concept**
Protamine sulfate is a medication used to reverse anticoagulation caused by heparin, a commonly used anticoagulant in medical settings. The mechanism of action involves binding to heparin to form a stable complex, thereby neutralizing its anticoagulant effects.

**Why the Correct Answer is Right**
Protamine sulfate works by forming a stable complex with heparin, which is a highly sulfated polysaccharide. This complexation reaction is facilitated by the positive charge on the protamine molecule, which binds to the negatively charged heparin molecule. The resulting complex is then rapidly cleared from the circulation, thereby reversing the anticoagulant effects of heparin. Protamine sulfate is the agent of choice for controlling heparin-induced bleeding because of its high efficacy and rapid onset of action.

**Why Each Wrong Option is Incorrect**
**Option A:** Vitamin K is used to reverse warfarin-induced bleeding, not heparin-induced bleeding. Although both anticoagulants work by inhibiting vitamin K-dependent clotting factors, they have different mechanisms of action and reversal agents.
**Option B:** Fresh frozen plasma (FFP) contains all the clotting factors and can be used to reverse anticoagulation caused by heparin, but it is not the agent of choice due to its high cost, potential for thrombosis, and need for cross-matching.
**Option C:** Activated charcoal has no role in reversing heparin-induced bleeding and is used primarily for gastrointestinal decontamination in cases of overdose.

**Clinical Pearl / High-Yield Fact**
When administering protamine sulfate to reverse heparin-induced bleeding, the dose should be titrated carefully to avoid excessive protamine administration, which can cause hypotension and cardiac arrest.

**Correct Answer:** C. Protamine sulfate.