Final answer:
The independent variable in this experiment is Exercise. It is the factor being manipulated to observe its effect on the dependent variable.
Step-by-step explanation:
The independent variable in this experiment is Exercise. The independent variable is the factor that is intentionally manipulated by the researchers in order to observe its effect on the dependent variable, which is the variable being measured or observed. In this case, the group of students is trying to determine the effect of exercise on pulse rate, so exercise is the independent variable.