Choose the right answer from the following:
Two identical blocks of iron, one at \[10{}^\circ C\] and the other at $20{}^\circ C$, are put in contact. Suppose the cooler block cools to $5{}^\circ C$ and the warmer block warms to $25{}^\circ C$. This would violate the _____.
1. Zeroth law of thermodynamics
2. First law of thermodynamics
3. Second law of thermodynamics
4. Third law of thermodynamics

Hint: To solve these types of questions, we must have a knowledge about all the laws of thermodynamics. We know that when two bodies at different temperatures are brought in contact with each other they come to an intermediate temperature. The intermediate temperature would lie closer to the body that has more mass.

Complete step by step answer:
Let us discuss all the laws of thermodynamics one by one to solve this question.
Zeroth law of thermodynamics- The zeroth law of thermodynamics states that two thermodynamics systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with one another.
First law of thermodynamics- The first law of thermodynamics states that energy is always conserved, it cannot be created or destroyed. Energy can only be converted from one form to another.
Second law of thermodynamics- The second law of thermodynamics states that the total change in entropy of any given system plus its surroundings will always make an increase in the spontaneous process.
Third law of thermodynamics- The third law of thermodynamics states that the entropy of perfectly crystalline solid approaches zero as the temperature approaches absolute zero.
According to the given question, second law of thermodynamics is violated because the if the cooler block cools to $5{}^\circ C$ and the warmer block warms to $25{}^\circ C$ then this would be a non-spontaneous process which is not true as the process when two identical blocks of iron, one at \[10{}^\circ C\] and the other at $20{}^\circ C$ is a spontaneous process.

Note: The fact that decides the final temperature of both the bodies is the mass of the constituent bodies. The intermediate temperature would lie closer to the body that has more mass. Suppose a small cup of water at \[10{}^\circ C\] is mixed with a bucket of at $20{}^\circ C$, then the final temperature would lie close to $20{}^\circ C$.