Following are statements of a few processes taking place in nature.
I. Free expansion of a gas
II. The combustion of a mixture of petrol and air ignited by a spark
III. The leaking of gas from the kitchen cylinder.
IV. The transfer of heat from one heated part of a liquid to the other colder part.
Which amongst these processes are irreversible in nature?

In thermodynamic processes, which of the following statements is not true?

The graph of pressure P and volume V of $1$ mole of an ideal gas at constant temperature is

Three metal rods of the same material and identical in all respects are joined as shown in the figure. The temperatures at the ends of these rods are maintained as indicated. Assuming no heat energy loss occurs through the curved surfaces of the rods, the temperature at the junction x is