During isothermal expansion of an ideal gas, the change in internal energy is ..............

Explanation

To determine the change in internal energy during the isothermal expansion of an ideal gas, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Isothermal Process**:
- An isothermal process is one in which the temperature (T) remains constant throughout the process. This means that the initial and final temperatures of the gas are equal (T1 = T2).

2. **Internal Energy and Temperature Relationship**:
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