Assertion: For an isothermal process in an ideal gas, the heat absorbed by the gas is entirely used in the work done by the gas
Reason: During a process taking place in a system, if the temperature remains constant then the process is isothermal?

A. Both assertion and reason are correct and reason is the correct explanation for assertion.
B. Both assertion and reason are correct and reason is not the correct explanation for assertion.
C. Assertion is correct but reason is incorrect.
D. Both assertion and reason are incorrect.

Hint: The isothermal process is a one of the processes in the cycles, one or two of the processes in the entire cycle (consists minimum of 4 processes) may be isothermal (depends upon the cycle). Isothermal meant that the temperature is constant through the process, it means no addition or rejection of temperature takes place.


Complete step by step answer
The process which follows the constant temperature is called the isothermal process, it says that the no addition of temperature and deduction of temperature happens to the gas. It also says that the internal energy will remain unchanged.
We can observe this type of process in the ideal cycles like Carnot.
So in the ideal gas cycle, the heat is absorbed by the gas for the work done, as there is no addition and removal temperature and internal energy remains constant.
Therefore, the assertion is correct and even the reason is also the correct statement in terms of the isothermal process (constant temperature and no change in internal energy)individually but the reason is not the correct explanation for the assertion provided, it means that the option (b) is correct.


Note: Here, we should be aware about the different processes, the isothermal process explains the constant temperature throughout the cycle, isentropic process explains the constant entropy in the cycle and isobaric process explains the constant pressure, isochoric process explains the constant volume process. We should not confuse between these 4 processes. All the processes are used in the cycle according to the cycle and to increase the output efficiency.