To solve this problem, we need to identify the curve that represents the adiabatic process.$\\$In a PV diagram:$\\$• An adiabatic process is steeper than an isothermal process.$\\$• An isothermal process follows $PV =$constant.$\\$• An adiabatic process follows $PV^{\gamma} =$constant, where $\gamma > 1. \\$Analyzing the given curves:$\\$• Curve 1 is vertical, indicating an isochoric process (constant volume).$\\$• Curve 4 is horizontal, indicating an isobaric process (constant pressure).$\\$• Curves 2 and 3 are downward sloping, indicating either isothermal or adiabatic processes.$\\$Since the adiabatic process is steeper than the isothermal process,$\\$curve 2 is steeper than curve 3.$\\$Therefore, curve 2 represents the adiabatic process.$\\$The correct option is 2.