What is an adiabatic process?

An adiabatic process is defined as one in which no heat is transferred into or out of the system during the process. This means that any work done by the system or on the system results solely from internal changes in energy, without any heat exchange with the surroundings. Such a process typically occurs in a well-insulated system or during rapid changes where heat exchange cannot take place significantly.

In the context of thermodynamics, if a gas is compressed adiabatically, all the work done on the gas increases its internal energy, leading to a rise in temperature without any heat being added from an external source. Similarly, during adiabatic expansion, the internal energy decreases as work is done by the gas against external pressure, leading to a drop in temperature.

The other choices describe different types of processes: a process with heat exchange or one with constant pressure or constant volume are not representative of the characteristics defining an adiabatic process. Hence, the correct understanding of an adiabatic process is that it strictly involves no heat transfer, confirming that option B is the correct choice.