(72 - 45) , (51 - 24) , (46 - 20) , (32 - 13)
Option:
Justification: This is the only group in which the two numbers have no common factor.

(72 - 45) , (51 - 24) , (46 - 20) , (32 - 13)
Justification: This is the only group in which the two numbers have no common factor.