Final answer:
Marijuana is the illicit drug most likely used by junior high school and high school students, due to its accessibility and sometimes varied legal status.
Step-by-step explanation:
The illicit drug most likely to be used by junior high school and high school students among the options provided is marijuana. Considering the accessibility and fluctuating legal status of marijuana in various jurisdictions, it is more commonly experimented with by teens compared to other substances like cocaine, heroin, LSD, and Ecstasy (MDMA). Recreational drugs like marijuana are sought after for their euphoric effects, though they can lead to adverse health consequences.
Ecstasy, also known as MDMA, is a mild stimulant with perception-altering effects and is also popular among some youth. Nonetheless, according to surveys and research studies, marijuana still remains the most widely used illicit substance by teens. It is important to acknowledge the risk of long-term cognitive and brain function impact from the use of such psychoactive substances during adolescence.