For irreversible expansion of an ideal gas under isothermal condition, the correct option is:

1. Isothermal condition ($\Delta T=0$): For an ideal gas, Internal energy ($U$) depends only on temperature. Thus, $\Delta U=n{C}_v\Delta T=0$.2. Irreversible expansion: For any irreversible process, the total entropy of the universe ($\Delta S_{total}=\Delta S_{sys}+\Delta S_{surr}$) must increase ($\Delta S_{total}>0$). It cannot be zero.Therefore, $\Delta U=0$ and $\Delta S_{total}\ne 0$.