Assertion: It is not possible for a system, unaided by an external agency to transfer heat from a body at lower temperature to another body at a higher temperature. Reason: It is not possible to violate the second law of thermodynamics.

Step-by-step solution

Second law of thermodynamics can be explained with the help of example of refrigerator, as we know that in refrigerator, the working substance extracts heat from colder body and rejects a large amount of heat to a hotter body with the help of an external agency i.e., the electric supply of the refrigerator. No refrigerator can ever work without external supply of electric energy to it.