For capacitors connected in series, the same charge \( Q \) is stored on both capacitors. The energy stored in a capacitor is given by \( E = \frac{1}{2} C V^2 \), where \( C \) is the capacitance and \( V \) is the potential difference across the capacitor. We calculate the energy stored in the first capacitor.
Step 2: Conclusion.
The energy stored in the capacitor of capacitance \( C_1 \) is 1600 \( \mu J \), corresponding to option (b).