Among the following, which is an atypical antipsychotic used in clinical practice?

Quetiapine is classified as an atypical antipsychotic, which means it is primarily used in the treatment of psychiatric conditions such as schizophrenia and bipolar disorder. Atypical antipsychotics are known for their ability to treat the symptoms of these disorders with generally fewer extrapyramidal side effects compared to typical antipsychotics.

Quetiapine works by affecting various neurotransmitter systems in the brain, including serotonin and dopamine receptors. This broad mechanism is part of what distinguishes atypical antipsychotics from their typical counterparts, as they tend to target multiple pathways rather than just dopamine receptors.

In contrast, Divalproex sodium is primarily used as a mood stabilizer and anticonvulsant rather than an antipsychotic. Haloperidol is a typical antipsychotic, associated with a higher incidence of strict movement-related side effects. Buspirone is an anxiolytic and does not fall under the category of antipsychotic medications. Therefore, recognizing Quetiapine as the atypical antipsychotic among the options is based on its recognized therapeutic use and mechanisms specific to that class of medications.