On the first day of class, Professor Wallace tells her geography students that pop quizzes will be given at unpredictable times throughout the semester. Studying for Professor Wallace's surprise quizzes will be reinforced on a schedule.

variable-interval                              

Explanation:

In psychology, a variable-interval schedule is described as a schedule of reinforcement which is considered as one of the parts in the operant conditioning and was discovered by B. F. Skinner. It is also denoted as VI, and is defined as a process whereby "reinforcement" is being given to a specific response only after a well-defined amount of time has been passed i.e, unpredictable time and therefore the amount of time is supposed to be on a variable or changing schedule.

As per the question, studying for professor Wallace's surprise quizzes will be reinforced on a variable-interval schedule.

aliens arent real sorry bud