C1 and C2 are in parallel. Their equivalent capacitance is in series with C3.
The stored charge separation is the same for each capacitor in series; the voltage difference of the equivalent capacitance is shared by the components.
The voltage difference is the same for each capacitor in parallel; the stored charge separation of the equivalent capacitance is shared by the components.
a) C1 is straightforward since it is connected directly to the battery.
b) To find the charge on C2, find the equivalent capacitance of the branch in which it lies. Then evaluate the charge and begin expanding the equivalent capacitance until the charge on C2 is determined.
Once the battery is disconnected, the stored charge separation will remain constant as the geometry of the capacitor is changed. Thus the voltage difference between the plates must change...