The principle applied in liquefaction of gases is

ANS:C - both (a) and (b).

Adiabatic Expansion: Adiabatic expansion refers to a process in which a gas expands without the exchange of heat with its surroundings. In other words, during adiabatic expansion, there is no transfer of thermal energy between the gas and its environment. This can occur rapidly, such as when a gas expands suddenly through a valve or a porous plug. During adiabatic expansion, the gas performs work on its surroundings as it expands, which leads to a decrease in its internal energy and temperature. This is because the energy used to do work comes from the internal energy of the gas, causing its temperature to drop. The decrease in temperature during adiabatic expansion can be described by the first law of thermodynamics, which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. Adiabatic expansion is often utilized in various engineering processes, such as in gas turbines, where the rapid expansion of hot gases generates mechanical work. Joule-Thomson Effect: The Joule-Thomson effect describes the change in temperature of a gas when it is allowed to expand through a valve or a porous plug while being kept insulated (adiabatic conditions). This effect is observed when a gas experiences a change in pressure and temperature as it flows through a restriction in a pipe or a porous medium. The Joule-Thomson effect can result in either cooling or heating of the gas, depending on its initial temperature, pressure, and the nature of the gas. If the gas is initially at a high pressure and then expands through the restriction, it typically experiences a decrease in temperature, leading to cooling. Conversely, if the gas is initially at a low pressure and then expands, it may experience an increase in temperature. This effect is widely used in various applications, including refrigeration and liquefaction of gases. In the context of liquefaction, the Joule-Thomson effect is crucial because it allows gases to be cooled to temperatures low enough for liquefaction by exploiting the temperature changes that occur during adiabatic expansion.