Capacitor C1is connected to a battery and charged till the magnitude of the charge on each plate is q0.Then, the battery is disconnected and C1is connected to two other uncharged capacitors  C2  and  C3 as shown (figure). Final charges on the capacitors  (q1,q2  and  q3) are related by

Initial situation after the reconnection is shown in figure (a) and the final situation in figure (b). The charge transferred by  C1 is q0−q1 and the capacitors  C2  and  C3 are in series, so  q2=q3.Other way to solve the questions is to equalize the potentials across C1and series combination of  C2  and  C3