Teacher: In this task, you are given a sentence. You are expected to recognize the name of any form of chemical substances. Although there might be several correct answers, you need to write one of them.
Teacher: Now, understand the problem? If you are still confused, see the following example:
Inhibition of the human ether-a-go-go-related gene (HERG) potassium channel by cisapride: affinity for open and inactivated states. 
Solution: potassium
Reason:  Potassium is a type of electrolyte mineral that helps our nerves to function and muscles to contract. Hence, it should be tagged as chemical.

Now, solve this instance: Reinforcement enhancing effects of nicotine via smoking.
Student:
nicotine