Final answer:
The statement is justified by the Transitive Property of Equality, which relates to the concept of equality in both math and thermodynamics.
Step-by-step explanation:
The given mathematical statement AB=MN and MN=PQ, so AB=PQ is justified by the Transitive Property of Equality. This property states that if a quantity A is equal to a quantity B, and B is equal to a quantity C, then A is also equal to C. In thermodynamics and mathematics, the properties of equality play crucial roles in demonstrating relationships between variables and in forming consistent statements.