We consider a thermodynamic system. If $\Delta U$ represents the increase in its internal energy and $W$ the work done by the system, which of the following statement is true?

Question

$\begin{array}{1 1} (1)\; \text{∆U = –W in an isothermal process} \\ (2)\; \text{∆U = W in an isothermal process}\\ (3)\; \text{∆U = –W in an adiabatic process} \\ (4)\; \text{∆U = W in an adiabatic process} \end{array}$