C option is wrong for the capacitor question. I have a proof as well as the explanation.
I ran a simulation on EveryCircuit. The potential across the 30 ohm resistor comes out to be 2.27 V just after closing S2 which corresponds to a current of 0.079 V (this is given by some leading coaching classes as well).
It is quite apparent that the charge on capacitors C1, C3 and C4 is 40 µC before switching making Potential difference across C1 as 4V which is given in option B. From here it can be concluded that just before closing S2 the potential difference across PQ is 4 V.
However, after closing S2 it cannot be said that the potential difference across PQ remains 4V, as current will start flowing across the branches containing capacitor C1 and capacitor C3. This means that there would be a potential drop across the resistors 70 Ω and 100 Ω resistors, but there would be no appreciable change in the potential difference across the capacitors just after closing the switch S2. This implies that the potential across PQ changes and does not remain 4V.
If we assume C is correct, we get from here that the potential difference across PQ is taken to be 4 V, which is wrong as proven above. Taking potential difference across PQ as 4 Volt would be a violation of the junction law or KCL, as branches containing C1 and C3 will then have zero current but branch containing capacitor C2 will have finite current. Hence option C is incorrect.
So please challenge this question.