Which of the following pairs is correctly matched with its description?

The pair matching LSD with its description as a hallucinogen is correct because LSD (lysergic acid diethylamide) is well-known for its psychoactive effects, which primarily include altering perception, mood, and thought processes. Hallucinogens like LSD can cause significant changes in sensory perception, leading to hallucinations and altered states of consciousness.

The other options do not align correctly with their respective descriptions. For example, heroin is classified as an opioid and has depressant properties, not stimulant. Fentanyl is a synthetic opioid, which is not the same as being classified as a natural opioid. Alprazolam is a benzodiazepine and is classified as a Schedule IV substance, whereas Schedule II substances include drugs with a high potential for abuse like some opioids. Therefore, the correct pairing identifies LSD distinctly as a hallucinogen.