For a $Carnot$ engine,the source is at $500 \ K$ and the sink at $300 \ K$. What is the efficiency of this engine?

Which of the following statements is correct?

The process with negative entropy change is

When the same quantity of heat is absorbed by a system at two different temperatures $T_{1}$ and $T_{2}$,such that $T_{1} > T_{2}$,the changes in entropy are $\Delta S_{1}$ and $\Delta S_{2}$ respectively. Then:

The total entropy change for a system and its surroundings increases,if the process is

State the limitation of the second law of thermodynamics.