**Core Concept**
The antidote for benzodiazepine toxicity is a medication that reverses the central nervous system depressant effects of benzodiazepines. Benzodiazepines act by enhancing the activity of the neurotransmitter gamma-aminobutyric acid (GABA) through the GABA_A receptor.

**Why the Correct Answer is Right**
Flumazenil, the correct answer, is a selective benzodiazepine receptor antagonist that competes with benzodiazepines for binding to the GABA_A receptor. By occupying the receptor site, flumazenil reverses the sedative, anxiolytic, and anticonvulsant effects of benzodiazepines. Flumazenil is used to treat benzodiazepine overdoses and reverse sedation after procedures such as sedation during endoscopy or general anesthesia.

**Why Each Wrong Option is Incorrect**
**Option A:** Naloxone is an opioid receptor antagonist and is used to reverse opioid overdose, not benzodiazepine toxicity.
**Option B:** Physostigmine is a reversible cholinesterase inhibitor that can be used to treat anticholinergic toxicity, but it is not an antidote for benzodiazepine toxicity.
**Option C:** Activated charcoal may be used to treat benzodiazepine overdose in a prehospital setting, but it is not a specific antidote for reversing benzodiazepine effects.

**Clinical Pearl / High-Yield Fact**
Flumazenil can cause seizures in patients with a history of seizure disorders, and it should be used with caution in these patients. Additionally, flumazenil can precipitate withdrawal symptoms in patients who are physically dependent on benzodiazepines.

**Correct Answer: A. Flumazenil**