In a series circuit, the total voltage is divided among the capacitors inversely proportional to their capacitance values. The voltage across a capacitor in series can be calculated using the formula $V = \frac{Q}{C}$, where $Q$ is the charge and $C$ is the capacitance. Given the capacitances, the 6 pF capacitor will have the smallest voltage drop, resulting in 2 V across it when the total voltage is 12 V.