Assertion`:-` During isothermal expansion of ideal gas, temp,
remain constant.
Reason`:-` In adiabatic process temp. remain const.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertiion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that during the isothermal expansion of an ideal gas, the temperature remains constant. This is true because, by definition, an isothermal process is one in which the temperature of the system does not change.

2. **Understanding the Reason**: The reason states that in an adiabatic process, the temperature remains constant. This statement is false. In an adiabatic process, there is no heat exchange with the surroundings, which can lead to a change in temperature as the gas expands or compresses.

3. **Applying the First Law of Thermodynamics**: The first law of thermodynamics is given by the equation:
\[ \Delta U = Q + W \]
- For an isothermal process, since the temperature remains constant, the change in internal energy (\(\Delta U\)) is zero. Therefore, \(Q = -W\), meaning the work done by the system is equal to the heat absorbed from the surroundings.
- For an adiabatic process, \(Q = 0\), so the equation simplifies to \(\Delta U = W\). This indicates that any work done on or by the system results in a change in internal energy, which typically leads to a change in temperature.

4. **Conclusion**: Since the assertion is true and the reason is false, we conclude that the assertion is correct, but the reason provided is incorrect.

### Final Answer:
- **Assertion**: True
- **Reason**: False