In the diagrams $(i)$ to $(iv)$,the variation of volume with changing pressure is shown. $A$ gas is taken along the path $ABCD$. The change in internal energy of the gas will be:

Four curves $A, B, C$ and $D$ are drawn in the adjoining figure for a given amount of gas. The curves which represent adiabatic and isothermal changes are

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

The graph shows a $P-V$ diagram where $A-B$ is an adiabatic curve. Choose the correct statement regarding the processes $AC$ and $BC$.

One mole of an ideal gas in initial state $A$ undergoes a cyclic process $ABCA$,as shown in the figure. Its pressure at $A$ is $P_0$. Choose the correct option$(s)$ from the following:
$(A)$ Internal energies at $A$ and $B$ are the same
$(B)$ Work done by the gas in process $AB$ is $P_0 V_0 \ln 4$
$(C)$ Pressure at $C$ is $\frac{P_0}{4}$
$(D)$ Temperature at $C$ is $\frac{T_0}{4}$

An indicator diagram is a ...........