Which combination of the following statements is correct? P: A gas cools upon expansion only when its Joule-Thomson coefficient is positive in the temperature range of expansion. Q: For a system undergoing a process, its entropy remains constant only when the process is reversible. R: The work done by a closed system in an adiabatic is a point function. S: A liquid expands upon freezing when the slope of its fusion curve on pressureTemperature diagram is negative.

Which combination of the following statements is correct? P: A gas coo

1.	Which combination of the following statements is correct? P: A gas cools upon expansion only when its Joule-Thomson coefficient is positive in the temperature range of expansion. Q: For a system undergoing a process, its entropy remains constant only when the process is reversible. R: The work done by a closed system in an adiabatic is a point function. S: A liquid expands upon freezing when the slope of its fusion curve on pressureTemperature diagram is negative.
A.	R and S
B.	P and Q
C.	Q, R and S
D.	P, Q and R
Answer» B. P and Q

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