**Core Concept**
GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter in the brain, playing a crucial role in reducing neuronal excitability. Sedatives with GABA-facilitating action work by enhancing the activity of GABA receptors, leading to a calming effect on the nervous system. However, not all GABA-facilitating sedatives exhibit anticonvulsant, muscle relaxant, or sleep-inducing properties.

**Why the Correct Answer is Right**
Zolpidem is a non-benzodiazepine sedative that selectively acts on the GABA_A receptor, specifically at the α1 subunit, which is involved in regulating sleep and arousal. Unlike benzodiazepines like diazepam (Option A), zolpidem does not possess significant anticonvulsant or muscle relaxant properties. Its mechanism of action is distinct from barbiturates like phenobarbitone (Option C), which also act on GABA_A receptors but have a broader spectrum of activity. Buspirone (Option D) is an anxiolytic agent that acts as a serotonin 5-HT1A receptor agonist, rather than a GABA facilitator.

**Why Each Wrong Option is Incorrect**
**Option A:** Diazepam is a benzodiazepine that exhibits anticonvulsant, muscle relaxant, and sedative properties due to its action on GABA_A receptors at various subunits.

**Option C:** Phenobarbitone is a barbiturate that, while acting on GABA_A receptors, has a broader spectrum of activity, including anticonvulsant and muscle relaxant effects.

**Option D:** Buspirone is an anxiolytic agent that does not facilitate GABA activity; instead, it acts as a serotonin 5-HT1A receptor agonist.

**Clinical Pearl / High-Yield Fact**
Zolpidem's selective action on the α1 subunit of the GABA_A receptor makes it a useful agent for treating insomnia, as it does not carry the same risks of dependence or cognitive impairment associated with non-selective GABA facilitators.

**✓ Correct Answer: B. Zolpidem**