Concept:
Work done in a thermodynamic process is
\[
W=\int P\,dV.
\]
Thus, work is done only when there is a change in volume.
Step 1: Find the work done in case (i).
The system changes from
\[
(P,V)
\rightarrow
(P,2V).
\]
Pressure remains constant.
Hence the process is isobaric.
\[
W=P(V_f-V_i).
\]
\[
W=P(2V-V).
\]
\[
W=PV.
\]
Therefore,
\[
\boxed{W_1=PV}.
\]
Step 2: Find the work done in case (ii).
The system changes from
\[
(P_1,V)
\rightarrow
(2P_1,V).
\]
Volume remains constant.
Hence the process is isochoric.
For constant volume,
\[
dV=0.
\]
Therefore,
\[
W=\int P\,dV=0.
\]
Thus,
\[
\boxed{W_2=0}.
\]
Step 3: Write the final result.
\[
\boxed{
W_1=PV,
\qquad
W_2=0
}
\]
Hence,
\[
\boxed{\text{Answer = (D)}}
\]