An ideal gas undergoes an isothermal expansion, doing 50 J of work on its surroundings. What is the change in the internal energy of the gas?

✓ Correct Answer: Option B

For an ideal gas, internal energy (ΔU) depends only on temperature. In an isothermal process, the temperature remains constant (ΔT = 0), therefore the change in internal energy (ΔU) is zero.