On a P-V diagram, the four processes starting from the same initial state can be identified by their slopes:

1. Isobaric process: Pressure remains constant, represented by a horizontal line (slope = $0$).
2. Isochoric process: Volume remains constant, represented by a vertical line (infinite slope).
3. Isothermal and Adiabatic processes: Both curves show an inverse relationship between pressure and volume. However, the magnitude of the slope of an isothermal process is $\frac{P}{V}$, whereas the magnitude of the slope of an adiabatic process is $\gamma\frac{P}{V}$. Since $\gamma > 1$, the adiabatic curve is steeper than the isothermal curve.

In the standard figure from the NEET 2022 question paper, the curves are numbered from the vertical (isochoric drop in pressure) to the horizontal (isobaric expansion) as 1, 2, 3, and 4 respectively. Curve 1 is vertical (isochoric) and Curve 4 is horizontal (isobaric). Between the remaining two, Curve 2 is steeper than Curve 3, indicating that Curve 2 represents the adiabatic process while Curve 3 represents the isothermal process.