The thermodynamic process, in which internal energy of the system remains constant is

An isothermal process is a thermodynamic process in which the temperature of a system remains constant. The transfer of heat into or out of the system happens so slowly that thermal equilibrium is maintained.

 $\Delta T=0, \Delta U=n{C}_V∆T=0$.

According to first law of thermodynamics,

$$\begin{gathered} ∆Q=∆U+∆W \\ \Rightarrow ∆Q=∆W \end{gathered}$$