In the hypothesis "students who study a list of terms in the morning, just after waking up, will recall more terms than students who study the list just before falling asleep," what is the independent variable?

Time of day.

Explanation:

Independent variable is one that influences another variable (the dependent variable) and directly influences the outcome of a specific hypothesis. To find out which variable is independent of the above research, just ask, what is influencing students to remember the terms of the list they study. According to this question we will realize that the time of day students begin to study the terms of the list influences the memory of these students. Because of this influence, we can conclude that the "time of day" is the independent variable.

I believe the answer is: time of day

Independent variable refers to a type of variable that would act as a control group in order to measure its causal effect relationship with the dependent variable. In the example above, the dependent variable is the number of terms that can be remembered.