A weight less piston divides thermally insulated cylindrical vessel into two equal parts. One contains one mole of an ideal gas with adiabatic exponent $\gamma$, the other is evaccuated. The initial gas temperature is $T_0$. The piston is released, the gas fills the whole volume of the container. The piston is slowly displaced back to the initial position. Like internal energy U, entropy is another state function of a gas whose change can be calculated as $\Delta S=\int \frac{dQ}{T}$, where dQ = Quantity energy in the form of heat which may be either absorbed or ejected by the gas at temperature T. If  $\Delta U_1,\Delta S_1$ denote change in internal energy, change in entropy in the free expansion, and $\Delta U_2,\Delta S_2$  changes in internal energy, change in entropy in the slow compression respectively, then which of the following are correct.