Answer:
Exposure to nicotine is the independent variable
Step-by-step explanation:
An independent variable is a factor that remains unchanged (by other factors in the experiment) throughout the course of an experiment. It can however be manipulated by the researcher. A dependent variable, on the other hand, is the factor being measured that relies on the independent variable. In the case above, exposure to 1 hr of nicotine intake forms the independent variable while the levels of hand steadiness, which will be measured, form the dependent variable.