Heroin, commonly called as smack is a/an :

The correct answer is Option (2) → Opioid

Option (2) Opioid — Correct. Heroin is diacetylmorphine, made from morphine of the poppy latex; opioids bind to opioid receptors in the nervous system and gut.

NCERT Extract:
Drugs and Alcohol Abuse – “Opioids are the drugs, which bind to specific opioid receptors present in our central nervous system and gastrointestinal tract. Heroin (Figure 7.7), commonly called smack is chemically diacetylmorphine which is a white, odourless, bitter crystalline compound. This is obtained by acetylation of morphine (Figure 7.7), which is extracted from the latex of poppy plant Papaver somniferum (Figure 7.8).”