what is the independent variable between placebo group, pulse/heart rate, amount of caffeine, number of subjects in each group, time pulse was taken, and groups with caffeine

Answer 1

In this scenario, it's important to note what exactly is the question the experiment is trying to answer. From the options that were listed, it seems the amount of caffeine is the independent variable -- you are trying to vary the amount of caffeine administered to the subjects in the group. As a result of the amount of caffeine given, you measure their pulse/heart rate by taking it at different times