**Core Concept**
The question is testing the student's knowledge of atypical antipsychotics, a class of medications used to treat psychiatric conditions such as schizophrenia and bipolar disorder. Atypical antipsychotics are characterized by their lower risk of extrapyramidal side effects compared to typical antipsychotics.

**Why the Correct Answer is Right**
The correct answer is an example of an atypical antipsychotic because it belongs to the second-generation antipsychotics, which primarily block dopamine D2 receptors and serotonin 5-HT2A receptors. This dual-action mechanism is responsible for their therapeutic effects and reduced side effect profile. The correct answer, **Risperidone**, is a widely used atypical antipsychotic that has a unique pharmacological profile, with a high affinity for serotonin receptors.

**Why Each Wrong Option is Incorrect**
**Option A:** Haloperidol is a typical antipsychotic that primarily blocks dopamine D2 receptors, leading to a higher risk of extrapyramidal side effects.
**Option B:** Lithium is a mood stabilizer used in the treatment of bipolar disorder but is not an antipsychotic medication.
**Option C:** Diazepam is a benzodiazepine anxiolytic that is not an antipsychotic medication.

**Clinical Pearl / High-Yield Fact**
Atypical antipsychotics like Risperidone have a lower risk of tardive dyskinesia, a debilitating side effect associated with long-term use of typical antipsychotics.

**Correct Answer:** C. Diazepam