An ideal gas undergoes a quasi static, reversible process in which its molar heat capacity C remains constant. If during this process the relation of pressure P and volume V is given by PVn = constant, then n is given by (Here CP and CV are molar specific heat at constant pressure and constant volume, respectively):
C=CV+R1−n⇒C−CV=R1−n→Lor C=CP−RR1−n⇒C−CP=nR1−n⇒C=CPC−CV=n