Two identical blocks of iron are placed in contact, one at 10°C and the other at 20°C. If the cooler block cools to 5°C and the warmer block warms to 25°C, this would violate the?

this is violation of II law of thermodynamics

Explanation:

As per 2nd law of thermodynamics we know that heat always flows from high temperature to low temperature

If heat flows from low temperature to high temperature then it is only possible when some external work is done on the system

So here it says that initially two blocks are at 10 degree C and 20 degree C

Now the cool object will become cooler and hot object becomes hotter

which shows that heat is flowing from low temperature to high temperature

So this is violation of II law of thermodynamics