Answer
Capacitor 1 and Capacitor 3 are not in series.
Work Step by Step
The potential $V$ due to the battery produces charge on the bottom plate of capacitor 3. That charge causes charge to shift from the top plate of capacitor 3. This charge can shift to the bottom plate of capacitor 1 or to the bottom plate of capacitor 2. Because there is more than one path for the shifting charge to move, Capacitor 1 and Capacitor 3 are not in series.
