During an adiabatic process, the pressure of a gas is proportional to the cube of its temperature. The value of $C_p/C_v$ for that gas is :

Question

$$\begin {array} {1 1} (a)\;\frac{7}{5} & \quad (b)\;\frac{4}{5} \\ (c)\;\frac{5}{3} & \quad (d)\;\frac{3}{2} \end {array}$$