Correct option (c) equilibrium between gas and liquid
Explanation:
From the graph, at point A, CO2 exists as a gas, As pressure is increased. the volume of the gas decreases along the curve AB. At B liquefaction of the gas starts. Hence. volume decreases rapidly along BC because liquid has much less volume than the gas. At point C, liquefaction is complete. Amount of gas
decreased = Amount of liquid formed or increased.
Because along horizontal line, gas converts into liquid.