Does the internal energy of an ideal gas change in an adiabatic process?

$A$ graph of pressure versus volume for an ideal gas for different processes is as shown. In the graph,curve $OC$ represents:

During an adiabatic process, the pressure is proportional to the cube of the temperature. Then ${C_p}/{C_v}$ is . . . . . . .

During an adiabatic process,if the pressure of a gas is found to be proportional to the cube of its absolute temperature,then the ratio of $\frac{C_p}{C_V}$ for the gas is:

In an adiabatic change,the pressure $P$ and temperature $T$ of a monoatomic gas are related by the relation $P \propto T^C$,where $C$ equals

$A$ rigid diatomic gas undergoes adiabatic change. Its pressure $P$ and temperature $T$ are related as $P \propto T^x$ where $x$ is (in $.5$)