GATE Mechanical Engineering (ME) 2019 Shift 1 Solved Paper

According to Ist law of thermodynamics
$\mathit{\delta }\mathit{Q}=\mathit{d}\mathit{U}+\mathit{\delta }\mathit{W}$
If the heat interaction is equal to the work interaction $\left({\mathit{Q}}_{1-2}={\mathit{W}}_{1-2}\right)$. Then, $\mathit{d}\mathit{U}=0$ or Internal energy $\left(\mathit{U}\right)$ is constant which is possible only in the case of isothermal process