Final answer:
The statement 'If MN = PQ, then MN = PQ' is justified by the Reflexive Property, which states that any quantity is equal to itself.
Step-by-step explanation:
The statement If MN = PQ, then MN = PQ is justified by the Reflexive Property. This property states that any mathematical quantity is equal to itself. Essentially, it reflects the idea that if you have an object or a value such as MN, it is inherently equal to itself without needing any further justification.