For an adiabatic process, pressure and volume are related as follows:
PV^k = constant
where k is the specfic heat ratio.
Since the right is a constant, we can write the equation as follows:
P1V1^k = P2V2^k
substituting the given values,
P2/P1 = 2.5
V1/V2 = 2
2.5 = 2^k
k = 1.32
Hope this answers the question. Have a nice day.
