**Core Concept:** Alcohol dependence is a clinical syndrome characterized by a range of symptoms including tolerance, withdrawal, and compulsive use despite adverse consequences. Various medications are used for alcohol dependence treatment.

**Why the Correct Answer is Right:** Nalmefene is a selective opioid receptor antagonist that primarily targets the μ-opioid receptor, which is involved in alcohol craving and withdrawal symptoms. It is approved for the treatment of alcohol dependence and helps reduce alcohol consumption and alcohol-related harms.

**Why Each Wrong Option is Incorrect:**

A. **Naltrexone (Option A)**: Naltrexone is an opioid receptor antagonist that targets both μ- and δ-opioid receptors. It is also used for alcohol dependence, but its mechanism does not focus solely on the μ-opioid receptor, making it an incorrect answer in this context.

B. **Aripiprazole (Option B)**: Aripiprazole is an atypical antipsychotic drug that primarily targets dopaminergic and serotonergic systems. It is not a selective μ-opioid receptor antagonist and is not used for alcohol dependence.

C. **Chlordiazepoxide (Option C)**: Chlordiazepoxide is a benzodiazepine that acts on the GABA-A receptor. While it may be used for alcohol dependence, its mechanism of action is different from naltrexone and nalmefene, making it an incorrect answer in this context.

D. **Varenicline (Option D)**: Varenicline is a nicotinic acetylcholine receptor antagonist used for smoking cessation but not for alcohol dependence. Its mechanism of action is unrelated to the μ-opioid receptor and alcohol dependence management.

**Clinical Pearl:** Naltrexone and nalmefene are the two primary medications used for alcohol dependence treatment. Naltrexone has more extensive effects on various opioid receptors, while nalmefene is a more selective μ-opioid receptor antagonist, making nalmefene the correct answer in this context.