For process 1, ∆U is positive, for process 2, ∆U is zero and for process 3, ∆U is negative. Find the parameters indicating x and y axes.

For process 2, ∆U = 0. It will be isothermal process.In options (a) and (b) temperature is indicated on x-axis. If temperature is shown on x-axis, isothermal process can­not be shown as otherwise shown in the question for pro­cess 2. Hence options (a) and (b) are not correct.            Obviously, option (c) is not correct.