Is the splitting of water an exothermic or an endothermic process?

For the $P-V$ diagram of a thermodynamic cycle as shown in the figure,processes $BC$ and $DA$ are isothermal. Which of the corresponding graphs is correct?

$A$ monoatomic gas at pressure $P$ having volume $V$ expands isothermally to a volume $3V$ and then adiabatically to a volume $81V$. The final pressure of the gas is $(\gamma = 5/3)$.

Three moles of an ideal gas $\left( {{C_P} = \frac{7}{2}R} \right)$ at pressure ${P_A}$ and temperature ${T_A}$ is isothermally expanded to twice its initial volume. It is then compressed at constant pressure to its original volume. Finally, the gas is compressed at constant volume to its original pressure ${P_A}.$ The correct $P-V$ and $P-T$ diagrams indicating the process are

The ratio of the specific heat capacities of a gas is $1.5$. When the gas undergoes an adiabatic process, its volume is doubled and its pressure becomes $P_1$. When the gas undergoes an isothermal process, its volume is doubled and its pressure becomes $P_2$. If $P_1 = P_2$, what is the ratio of the initial pressures of the gas when it undergoes adiabatic and isothermal processes?

An ideal gas exists in a state with pressure $P_0$, volume $V_0$. It is isothermally expanded to $4$ times its initial volume $(V_0)$, then isobarically compressed to its original volume. Finally, the system is heated isochorically to bring it to its initial state. The amount of heat exchanged in this process is