In \(P\) versus \(V\) graph, the horizontal line is found in which ____ exists.

From the graph, at point \(A, \mathrm{CO}_2\) exists as a gas, As pressure is increased, the volume of the gas decreases along the curve \(A B\). At \(B\) liquefaction of the gas starts. Hence, volume decreases rapidly along \(B C\) because liquid has much less volume than the gas. At point \(C\), liquefaction is complete. Thus, along horizontal line, gas converts into liquid.