Final answer:
The Transitive Property of Equality justifies the statement ab=mn and mn=pq, so ab=pq.
Step-by-step explanation:
The property that justifies the statement ab=mn and mn=pq, so ab=pq is the Transitive Property of Equality.
The Transitive Property of Equality states that if two things are equal to the same thing, then they are equal to each other.
In this case, since mn is equal to pq and ab is equal to mn, we can conclude that ab is equal to pq.