Assertion : During an adiabatic process, heat energy is not exchanged between system and its surroundings. Reason : The temperature of a gas increases when it undergoes an adiabatic expansion.

Step-by-step solution

In adiabatic process, no heat enters or leaves the system. The system is completely insulated from its surroundings. From first law of thermodynamics, change in internal energy, E=q-W=0-W=-W . Since the work is done at the expense of internal energy, therefore internal energy of the system decreases and hence temperature of the gas falls.