Which of the following is an isolated system?

$A$ system goes from $A$ to $B$ via two processes $I$ and $II$ as shown in the figure. If $\Delta U_1$ and $\Delta U_2$ are the changes in internal energies in the processes $I$ and $II$ respectively,then:

Under which of the following conditions is the relation $\Delta H = \Delta E + P \Delta V$ valid for a closed system?

The total internal energy change for a reversible isothermal cycle is

The heat of combustion of ethanol in a bomb calorimeter at $25\,^oC$ is $-670.48\, K\,cal\, mol^{-1}$. Find the value of $\Delta U$ in $K\,cal$ for the reaction at $25\,^oC$.

The work done during reversible isothermal expansion of one mole of hydrogen gas at $25^{\circ}C$ from a pressure of $20 \ atm$ to $10 \ atm$ is
(Given $R = 2.0 \ cal \ K^{-1} \ mol^{-1}$)