Assertion: An isothermal process is always an isolated one.
Reason: During an isothermal change, there exists thermal equlibrium between system and surroundings.

Options

A. Statement-I is true, statement-II is true and statement-II is correct explanation for statement-I
B. Statement-I is true, statement-II is true and statement-II is NOT correct explanation for statement-I
C. Statement-I is true, statement-II is false
D. Statement -I is false, statement-II is true.

Answer

To solve the assertion-reason question, we need to evaluate both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states: "An isothermal process is always an isolated one."

- An **isothermal process** is defined as a process that occurs at a constant temperature.
- In this type of process, there is heat exchange between the system and its surroundings to maintain the temperature.
- Therefore, an isothermal process is **not** an isolated process because an isolated process is one where no heat or matter is exchanged with the surroundings.

**Conclusion for Assertion**: The assertion is **false**.

### Step 2: Analyze the Reason
The reason states: "During an isothermal change, there exists thermal equilibrium between system and surroundings."

- During an isothermal process, the temperature of the system remains constant.
- For the temperature to remain constant, the system must exchange heat with its surroundings to balance any internal energy changes.
- This exchange leads to thermal equilibrium, meaning that the temperature of the system and the surroundings is the same.

**Conclusion for Reason**: The reason is **true**.

### Final Conclusion
- The assertion is false, and the reason is true. Therefore, the correct option is that the assertion is false and the reason is true.