Which of the following processes is correct for a given P-V diagram?
 
A) Adiabatic process
B) Isothermal process
C) Isobaric process
D) Isochoric process

Hint: The curve given to us is a P-V curve. It represents the changes in pressure and volume for a gas in a container of fixed volume, free to be compressed and to expand. There are other curves such as the P-T curve that represents the variations in pressure and temperature, and V-T curve that represent the changes between volume and temperature of the gas.

Complete step by step solution:
In the given figure, the line is parallel to the x-axis, which implies that the quantity given on the y-axis is constant for any variation in the quantity given on the x-axis. The quantity on the y-axis is pressure. This implies that the given curve represents a process in which there is no pressure change or the pressure remains constant throughout.

Such a thermodynamic process is called an isobaric process. A very common example of an isobaric process is cooking in an open vessel, such as we do in our kitchen. The pressure over an open vessel is always equal to the atmospheric pressure and is thus constant. The volume might decrease or increase, this means that the line can progress towards the positive x-axis and the negative x-axis, but it will always remain parallel to the x-axis with the same y-intercept.

Hence, option (C) is the correct answer.

Note: If we plot other graphs for isobaric processes, with variations between other physical quantities, we’ll get different results. A graph between the temperature and the volume for an isobaric process will give us a straight line passing through the origin. This shows that variations in other quantities are different from the variation in pressure or volume for any thermodynamic process.