Refer to figure given below. Let $ΔU_1$ and $ΔU_2$ be the change in internal energy in processes $A$ and $B$ respectively, $ΔQ$ be the net heat given to the system in process $A + B$ and $ΔW$ be the net work done by the system in the process $A + B.$

     
For the above figure:

Choose the correct option:
1. (a), (b) 
2. (b), (c) 
3. (c), (d) 
4. (a), (c) 

A thermodynamic system undergoes a cyclic process $ABCDA$ as shown in Fig. The work done by the system in the cycle is: 
             
1. $P_0 V_0$
2. $2 P_0 V_0$
3. $\frac{P_0 V_0}{2}$
4. zero

The quantity of heat required to take a system from $\mathrm{A}$ to $\mathrm{C}$ through the process $\mathrm{ABC}$ is $20$ cal. The quantity of heat required to go from $\mathrm{A}$ to $\mathrm{C}$ directly is: